Bosch Tankless Water Heater Maintenance Guide [Gas & Electric]

The annual maintenance on a Bosch tankless water heater typically includes:

  • Checking the combustion chamber
  • Inspecting the venting system
  • Checking the water inlet filter
  • Testing the pressure relief valve
  • Cleaning the heat exchanger’s fin coils
  • Sorting freeze damage
  • Cleaning inlet filter screen

Apart from these maintenance tasks, periodic descaling and winterizing are important tasks to maintain the performance and extend the lifespan of your Bosch tankless water heater. Therefore, in this article, let’s take a closer look at some of the important Bosch tankless water heater maintenance points for both gas and electric that you should consider.

Maintenance Table for Bosch Gas Tankless Water Heater

Blockages in the venting system# Check burner flames for steady and blue flames, address yellow or inconsistent flames immediately
# Ensure proper combustion and a working ventilation system.
Cracked combustion chambers# Check the burner observation window for cracks or gas flues.
# Check that the exhaust system and combustion air supply meet the manufacturer’s specifications.
Faulty pressure relief valves# Examine the pressure relief valve to ensure proper operation and discharge to a safe location.
Clogged inlet water filters# Examine and clean the inlet water filter on a regular basis to ensure proper water flow and efficiency.
Water Valve Problems# Lubricate the water valve components regularly to prevent wear and debris buildup.
# Clean or replace clogged components to restore proper water flow and heat transfer.
# Lubricate seals and gaskets to prevent deterioration and brittleness.
# Inspect and replace damaged seals or gaskets to prevent leaks around the valve assembly.
# Apply lubrication to moving parts, such as the pushrod and o-ring, to prevent sticking and ensure smooth operation of the valve.
# Properly lubricate and rebuild the water valve to ensure it functions correctly in controlling water flow to the heat exchanger.
Buildup on the heat exchanger# Periodically check the heat exchanger for scale buildup and descale as necessary.
Pilot Light Problems# Clean the pilot assembly to remove dirt, dust, or debris that may obstruct the gas flow and affect the quality and size of the pilot flame.
# Soak the pilot orifice and gas tubing in carburetor cleaner, then dry them thoroughly to remove any blockages.
# Use the correct orifice size and gas-to-air ratio for the specific gas type (e.g., natural gas or propane).
# Verify the gas type compatibility and adjust the orifice accordingly for optimal combustion.
Soot buildup on heat exchanger coils# Inspect the heat exchanger’s fin coils for soot accumulation or obstructions.
# Follow the manufacturer’s instructions for the descaling process. 
# Clean the fin coils as required.
Blocked Condensate Siphon
# Consult a professional plumber for maintenance if needed.
# Regularly inspect and clean the condensate siphon to ensure proper functioning.

Maintenance Table for Bosch Electric Tankless Water Heater

Maintenance StepDescription
Freeze damage to water heater# Ensure proper drainage of the water heater to prevent freeze damage.
# Consider adding antifreeze measures to protect the water heater from freezing.
# Thoroughly drain the water heater, including the heat exchangers and connecting pipes, to ensure complete drainage.
Checking the inlet filter screen# Check the inlet water filter screen annually to prevent clogging and maintain efficiency.
# Regularly cleaning the filter helps reduce strain on components and extend the lifespan of the water heater.
# Always disconnect the electric supply before performing maintenance tasks to ensure safety.
# Disconnect the cold and hot water pipes carefully, using appropriate tools, and collect the draining water in a container.
# Remove the filter, clean it with water, and inspect for damage or clogging.

Bosch Tankless Water Heater Maintenance Guide

Regular maintenance of your Bosch tankless water heater is essential for ensuring optimal performance, energy efficiency, and longevity of the unit.

bosch tankless water heater maintenance

In this guide, I will walk you through the steps involved in annual maintenance. Additionally, I’ve separated the maintenance sections for gas and electric water heaters to make things easier for you.

1. Bosch Gas Water Heater Maintenance

i) Blockage In Venting System

The combustion air inlet pipe is responsible for providing the unit with fresh air for proper combustion, while the exhaust termination removes exhaust gases from the unit. Any blockages or debris in these components can impact the efficiency and safety of the unit.

If the combustion air inlet pipe is blocked or obstructed, it can limit the amount of air that reaches the combustion chamber, which can lead to incomplete combustion and reduced efficiency. Similarly, if the exhaust termination is blocked, it can restrict the flow of exhaust gases, leading to a buildup of carbon monoxide and other harmful gases within the unit.

How To Fix:

Observing the burner flames during operation is an important part of maintaining a Bosch tankless water heater. The burner flames should be steady and blue, which indicates that the unit is functioning properly and efficiently.

If you notice yellow or inconsistent flames, this could be an indication of poor ventilation or a problem with the combustion air supply. Poor ventilation can cause a buildup of carbon monoxide and other harmful gases within the unit, which can be a serious health hazard. It’s important to address any issues with burner flames immediately and seek professional help if necessary.

ii) Cracked Combustion Chamber

Cracks can develop in the combustion chamber due to the expansion and contraction of the metal as it heats up and cools down. The burner observation window allows you to observe the burner flames and check for any cracks or flues of gases during the combustion process. 

Cracks in the window can allow flue gases to escape from the unit, which can be a safety hazard. Spillage of flue gases can also be an indication of poor ventilation or other issues with the unit.

How To Fix:

As a part of regular maintenance, you should inspect the burner observation window for cracks or flue gas spillage, and ensure that the burner flames are steady and blue with no signs of yellowing, which indicates proper combustion. It’s important to verify that the exhaust system and combustion air supply meet the manufacturer’s specifications to ensure proper combustion and prevent safety hazards.

iii) Faulty Pressure Relief Valve

The pressure relief valve is responsible for releasing pressure buildup within the water heater, which helps prevent dangerous explosions or leaks.

If the pressure relief valve is faulty or not functioning properly, it can result in a buildup of pressure within the water heater that can cause damage or safety hazards.

How To Fix:

Verifying the correct functioning of the pressure relief valve is crucial, and it can be done by manually opening it. When the valve is opened, it’s important to ensure that the discharge drains away safely. This means that the water should be directed to a safe location, such as a drain or bucket, and not allowed to pool around the water heater or in areas where it could cause damage.

In summary, while it’s important to manually open the pressure relief valve to ensure proper operation, it’s ideal to let a certified plumber handle this task to ensure safety and proper execution.

iv) Clogged Inlet Water Filter

The inlet water filter is designed to remove dirt, debris, and other contaminants from the water before it enters the water heater. If the filter becomes clogged or damaged, it can cause a reduction in water flow and affect the efficiency of the water heater.

How To Fix:

I have explained all the steps on how to clean your inlet filter on your Bosch tankless water heater below. So let’s dive in.

Step 1: Shut off the cold water isolation valve to the heater, if it is not already installed, install one before proceeding.

Step 2: Open the hot water tap nearest to you in order to drain the plumbing lines.

Step 3: Place a bucket under the water valve assembly of the heater to catch any water that may drain from it.

Step 4: Remove the retaining clip located at the base of the water valve assembly. Next, you should detach the brass hex cap that holds the inlet filter in place and remove the threaded bushing to gain access to the cylindrical filter inside.

Step 5: If the filter appears to be dirty or clogged, you can clean it using a soft-bristled brush or by gently washing it with water. If the filter is damaged in any way, it should be replaced with a new one.

v) Faulty Water Valve

A faulty water valve can give you serious headaches as it can cause several other problems with your heater. Here is a list of the problems:

Decreased Performance: Over time, the components of the water valve may wear down or become clogged with debris, affecting its functionality. This can result in decreased water flow, reduced heat transfer, and ultimately lower performance from the heater.

Leaks: Lack of lubrication can cause seals and gaskets within the water valve to deteriorate or become brittle. This can lead to leaks around the valve assembly, causing water to escape and potentially causing water damage to the surrounding area.

Valve Sticking: A faulty water valve can cause the moving parts of the water valve, such as the pushrod and o-ring, can become sticky or seize up. This can result in difficulties with opening or closing the valve, affecting water flow and the overall operation of the heater.

Malfunctioning Heat Exchanger: The water valve is responsible for controlling the flow of water into the heat exchanger. If the valve is faulty, it may not function correctly, leading to insufficient water circulation within the heat exchanger. This can cause the heat exchanger to overheat, potentially leading to damage or a complete breakdown of the unit.

How To Fix:

If you want to solve the above problems then lubrication and rebuilding your water valve is necessary. You can follow the guide to troubleshoot these issues.

Before you begin, make sure to shut off the installer-supplied cold water isolation valve to the heater. If there is no isolation valve installed, it should be installed before proceeding. Follow these steps to lubricate and rebuild the water valve:

Step 1: Open the nearest hot water tap to drain the plumbing lines and relieve any pressure in the system. Place a bucket or container under the heater’s water valve assembly to catch any water that may drain from the heater during the process. Locate the inlet water pipe connected to the back of the water valve and disconnect it carefully.

Step 2: Similarly, remove the retaining pin on the water valve assembly. Pull the pipe free to disconnect the water pipe leading from the water valve to the heat exchanger. Next, locate the two set screws at the bottom of the water valve where it connects to the gas valve. Loosen these set screws. If they are seized or difficult to loosen, stop immediately and contact Bosch tech support for assistance. Forcing or snapping seized set screws can cause irreversible damage to the water valve and gas valve assemblies.

Step 3: Once the set screws are loosened, remove the water valve by pulling it to the right. Separate the two halves of the water valve by removing the five screws on the left side of the water valve. Apply lithium grease or faucet & valve grease to the pushrod and o-ring. This lubrication helps ensure the smooth operation of the water valve. Inspect the venturi, which is a small tube-like component in the water valve. Clean the venturi if necessary to remove any debris or buildup that may impede its functioning. Refer to Fig. 27 in the provided instructions for visual guidance.

Step 4: Now, it’s time to rebuild the water valve. Several parts within the water valve should be replaced every 3 to 5 years, depending on water quality and usage. Consult the parts list and instructions on the Bosch website for the specific parts needed and detailed rebuilding steps.

Step 5: Assemble the two halves of the water valve by aligning them and securing them with the screws removed earlier. Reconnect the water pipe leading out of the water valve to the heat exchanger and secure it with the retaining pin. Reconnect the inlet water pipe to the back of the water valve. Tighten the set screws at the bottom of the water valve where it connects to the gas valve securely.

Step 6: Close the hot water tap that was opened earlier to drain the plumbing lines. Turn on the installer-supplied cold water isolation valve to restore the water supply to the heater. Check for any leaks around the water valve and ensure the proper functioning of the rebuilt water valve. Regularly monitor and maintain the water valve to prevent any issues and ensure optimal performance of the heater.

vi) Pilot Light Problem

When the pilot flame is not burning with a clean, sharp blue flame and does not fully engulf the tip of the thermocouple, it indicates a potential problem with the pilot assembly. Here are the possible reasons for the problems:

  • Pilot Assembly Blockage: Over time, the pilot assembly can accumulate dirt, dust, or debris, leading to blockages that obstruct the proper flow of gas. These blockages can affect the quality and size of the pilot flame.
  • Clogged or Damaged Pilot Orifice: The pilot orifice, which controls the gas flow to the pilot assembly, may be clogged with debris or damaged. This can result in an improper flame, as the orifice is responsible for regulating the amount of gas reaching the pilot burner.
  • Improper Gas Type: Using the wrong type of gas (e.g., natural gas instead of propane or vice versa) can cause issues with the pilot flame. Each gas type requires a specific orifice size and gas-to-air ratio for optimal combustion.

How To Fix:

To clean and reassemble the pilot assembly, follow these steps. First, shut off the gas supply using the manual gas shutoff valve. Locate the pilot gas tubing and release it from the retaining clip at the base. 

Push upward on the other end to detach it from the burner mount. Remove the brass hex-headed pilot orifice from the gas valve. Soak the orifice and pilot gas tubing in carburetor cleaner for 30 minutes, then dry them thoroughly. 

Reinsert the orifice into the gas valve, ensuring it is aligned properly. If it’s an LP unit, use the appropriate orifice. Reinstall the pilot gas tubing, securing it to the burner mount. Open the gas supply and relight the pilot following the manufacturer’s instructions. Observe the pilot flame, which should burn with a clean blue flame fully engulfing the thermocouple.

If you want detailed information about these troubleshooting steps, you can check out our Bosch tankless water heater pilot light troubleshooting guide.

vii) Buildup On Heat Exchanger

Scale build-up on the heat exchanger is a common problem with tankless water heaters, including Bosch tankless water heaters. This happens due to the accumulation of minerals such as calcium and magnesium in the water, which can cause scaling on the heat exchanger. As the scale builds up, it reduces the efficiency of the heater and can cause damage to the unit.

How To Fix:

Checking the heat exchanger for scale buildup should be done periodically, depending on the hardness of the water in your area. If the water is very hard, meaning it contains a high level of minerals such as calcium and magnesium, then regular descaling of the heat exchanger may be necessary to prevent excessive scale buildup. 

It is important to use the appropriate descaling solution to avoid damaging the unit. Well, we have a detailed section about this topic in the later part of this Bosch tankless water heater maintenance guide. 

viii) Soot Build-up On Heat Exchanger’s Fin Coils

Over time, the heat exchanger can accumulate soot and debris, which can reduce its efficiency and even cause damage to the system. Soot build-up can result from incomplete combustion and can cause reduced efficiency, higher energy costs, and even dangerous conditions such as carbon monoxide emissions.

How To Fix:

Inspecting the heat exchanger fin coils for soot build-up or blockage is an important step in maintaining a Bosch tankless water heater. It is recommended to follow Bosch tankless water heater manual or contact Bosch tankless water heater customer service to access the heat exchanger fin coils.

If you notice any signs of soot accumulation or blockage, it is necessary to have a qualified technician remove and clean the heat exchanger thoroughly. It’s important to ensure that the installation and adjustment of the water heater are made correctly to avoid damage to the unit. 

If there is an issue with the venting, gas pressure, or flue gases, it should be examined to determine the cause and address it appropriately.

ix) Blocked Condensate Siphon

A blocked or malfunctioning condensate siphon can cause problems with the operation of a tankless water heater. If the siphon becomes blocked, it can prevent condensate from draining properly, leading to water backup, leaks, and potentially even system shutdown. 

How To Fix:

To ensure the proper functioning of the condensate siphon, it is important to check it regularly and make sure it is free from any dirt or debris that could cause a blockage. This can be done by visually inspecting the siphon and removing any blockages found.

In case of any doubts or difficulties, it is advisable to consult a professional plumber or the customer service department of Bosch water heaters.

x) Air Filter Cleaning

To address potential issues with the air filter, it is important to verify if the filter is clean and undamaged. The air filter is typically attached to the fan assembly of the water heater. A clogged air filter in a water heater can lead to various problems that affect its performance and efficiency. Here are some issues that can arise due to a clogged air filter:

  1. Reduced airflow
  2. Overheating
  3. Poor water quality
  4. System malfunctions or shutdown

How To Fix:

Regular maintenance of the air filter is necessary to ensure proper airflow and prevent clogging. If the filter is found to be clogged or damaged, it should be cleaned or replaced accordingly. To disconnect the electrical supply from the water heater and remove the air filter, follow these steps:

Step 1: Firstly, you have to remove the front cover. Front cover removal is an important task in the maintenance process. So you have to do it very carefully. You can follow the below steps so that you can remove the front cover very easily:

  • Locate and loosen two Phillips head screws located on the bottom of the unit.
  • Disconnect the wire from the HMI (display).
  • Lift the front cover to remove it from the appliance.
  • Install the appliance in a vertical position. 

Step 2: Safely disconnect the electrical supply to the water heater. This may involve turning off the circuit breaker or unplugging the power cord, depending on the specific setup.

Step 3: Once the front cover is removed, you should be able to access the air filter. Look for two Philips head screws that secure the air filter in place.

Step 4: Use a screwdriver to loosen and remove the two Philips head screws. Set the screws aside in a safe place.

Step 5: With the screws removed, carefully lift and remove the air filter from the fan assembly. Take note of its position and orientation for reassembly.

Step 6: To reassemble, follow the steps in reverse order. Place the air filter back into position on the fan assembly, ensuring it is aligned correctly. Then, reattach the two Philips head screws and tighten them securely.

Step 7: Finally, reattach the appliance front cover by following the instructions provided in the manual. Make sure it is properly aligned and securely fastened.

2. Bosch Electric Water Heater Maintenance

i) Solving The Freeze Damage Problem

The harm caused by the freezing of water within the system is referred to as freeze damage to a water heater. When water freezes, it expands, and this expansion can lead to various types of damage. Freeze damage to a water heater can occur for the following reasons:

bosch electric tankless water heater
  1. Incomplete drainage: As mentioned, it can be challenging to completely drain the water from the heater due to the shape of the heat exchangers and connecting pipes. This could leave residual water in the system, which can still freeze and potentially cause damage.
  1. Limited mention of antifreeze measures: The procedure focuses primarily on draining the water from the heater, but it does not mention the use of antifreeze measures, such as adding non-toxic antifreeze solutions to the system. Antifreeze can help lower the freezing point of the remaining water and provide extra protection against freeze damage.

How To Fix:

To best minimize the chance of freeze damage and drain the heater, follow these steps:

Step 1: Disconnect the electric supply: Before starting any work, ensure the heater is completely disconnected from the power source. This step is crucial for safety purposes.

Step 2: Disconnect the cold and hot water pipes: Locate the fittings on the bottom of the heater where the cold and hot water pipes are connected. Use appropriate tools to loosen and disconnect these pipes.

Step 3: Allow the water to drain out: Once the pipes are disconnected, water will start to flow out of the heater. It’s essential to have a catch basin or container in place to collect the water and prevent any water damage. The process may take some time, as it can be challenging to remove all the water due to the shape of the heat exchangers and connecting pipes.

ii) Inspecting The Inlet Filter Screen

Checking the inlet water filter screen once a year is recommended for proper maintenance of your water heater. Here’s why it is important:

  1. Prevents clogging: The inlet water filter screen is designed to trap debris and sediment from the water supply. Over time, these particles can accumulate and clog the filter. Checking the filter annually allows you to remove any buildup, ensuring a consistent flow of clean water into the heater.
  2. Maintains efficiency: A clogged filter restricts the water flow into the heater, which can reduce its efficiency. By regularly inspecting and cleaning the filter, you can optimize the performance of your water heater and maintain its energy efficiency.
  3. Extends the lifespan of the heater: When the filter is clogged, it puts extra strain on the heater’s components, such as the heat exchanger. This can lead to increased wear and tear, potentially shortening the lifespan of the heater. By keeping the filter clean, you can help prolong the life of the unit.

How To Fix:

The below steps outline the procedure for checking and maintaining the inlet water filter screen of a water heater:

Step 1: Check that the power is switched off at the circuit breaker panel. Ensuring the power is turned off at the circuit breaker panel prevents any risk of electric shock while performing maintenance tasks.

Step 2: Shut off the installer-supplied cold water isolation valve to the heater. If a cold water isolation valve is present, it should be shut off before proceeding. This valve stops the water supply to the heater, allowing for safe maintenance. If one is not installed, it is recommended to have one installed. Open the nearest hot water tap to relieve pressure in the plumbing lines. This step helps release any built-up pressure in the plumbing lines, making it safer to work on the water heater.

Step 3: Position a bucket under the cold water inlet connection. Placing a bucket under the cold water inlet connection of the heater catches any water that may drain during the maintenance process, preventing water damage.

Step 4: Disconnect the cold water plumbing connection from the inlet which accesses the filter screen. Remove the filter, clean it with water, and inspect for damage. If the filter is damaged, it should be replaced.

Step 5: Replace the filter into the inlet housing. Once cleaned and inspected, place the filter back into the inlet housing. 

Important notes: Do not leave the filter out, as it is necessary for proper functioning. Do not remove the flow regulator located behind the filter. Do not attempt to clear the filter by backflushing, as it may damage the heater. Never use an air line to blow out the heater, as it can permanently damage the flow transducer.

Step 6: Before switching the power back on, reconnect the cold water plumbing connection. Once the filter is in place, reconnect the cold water plumbing connection to the heater. Open all hot water taps and inspect each tap to purge air from the line. Open all hot water taps and allow the water to flow until all air in the lines is purged. This ensures proper water flow and avoids airlocks.

Step 7: Turn on all circuit breakers supplying the water heater. With the taps still flowing and the air purged from the lines, switch on all circuit breakers supplying power to the water heater. Close all the hot water taps once the air is purged, and the water is flowing smoothly. The water heater is now ready for normal operation.

Step 8: Depending on the specific water heater model, you may need to adjust the maximum flow rate settings if necessary.

Do’s And Don’t’s While Maintaining Bosch Tankless Water Heater

Here are some general do’s and don’ts to keep in mind while maintaining your Bosch tankless water heater:


  • Schedule annual maintenance with a qualified technician to ensure optimal performance and efficiency.
  • It is generally recommended to have a professional inspect and service your complete water heating system, including the Bosch tankless water heater, once a year.
  • It is important to regularly inspect the water heater and its components for any signs of wear or fatigue. If you notice any faults, such as leaks, unusual noises, or fluctuations in water temperature or pressure, it is important to have them repaired immediately by a qualified technician.
  • If you are not sure how to safely shut off the power, gas, or water, seek the assistance of a qualified professional.  


  • Don’t start servicing without shutting off the electric supply.
  • Before performing any maintenance work, ensure that you have shut off the manual gas valve and the water valves. Remember to only turn the equipment back on after the servicing is complete and you have confirmed that it is safe to do so.

Extra Tips:

Whenever your appliance displays error codes A1, A5, and E5, it is generally recommended to proceed with heat exchanger descaling. These error codes are often an indication of scaling in the heat exchanger.  Also, it can reduce the efficiency of the appliance and potentially lead to overheating. Check out our guide on Bosch tankless water heater error codes to learn more about them.

If you are experiencing error code CE on your appliance, it is recommended to proceed with cleaning the heat exchanger fin coils. This error code often indicates a problem with the appliance’s combustion process, which can lead to the accumulation of soot and debris on the heat exchanger fins.

A water softener is recommended for areas with high water hardness, typically defined as exceeding 6 grains per gallon (or 180 mg/l) of calcium carbonate.  

The use of substances like anti-freeze is strictly prohibited and will nullify the warranty as they can result in harm to the internal components of the water heater.

Mandatory Annual Maintenance Table

Performing regular maintenance on your water heater is essential to ensure that it operates at peak performance and to increase its lifespan. By following a regular maintenance schedule, you can ensure that your water heater operates efficiently and reliably, providing you with hot water whenever you need it.

Parts to be MaintainedEvery Year
Check Heat ExchangerNecessary
Examine Pressure ReliefNecessary
Evaluate Combustion ChamberNecessary
Inspect Water FilterNecessary
Inspect BurnerNecessary
Test Condensate TrapNot Necessary
Heat Exchanger DescalingOnce 
Fin Coils         Once or Twice

How To Descale The Bosch Tankless Water Heater?

You should descale the heater at periodic intervals. You’d have to do it more often in areas that have a hard water supply. The mineral deposits inside the heat exchanger can make it less efficient. This issue can also trigger error codes like AA, E3, or A5.

There are many other error codes that can pop up in your Bosch tankless heater. To learn in detail you can check out our “comprehensive Bosch tankless error codes guide” that is linked above.

Descaling involves flushing out the unit with a descaling solution to remove mineral buildup and restore optimal performance. Regular descaling can help extend the lifespan of the unit and prevent issues caused by mineral buildup. I’ll assist you with the step-by-step process of descaling the heat exchanger.

Step 1: To start the maintenance process for the Bosch tankless water heater, begin by disconnecting the electrical supply and shutting off the water supply. It is important to open the hot water taps to drain the plumbing system and release any built-up pressure. Once the plumbing system is drained, you should turn off the hot water valve that leads to the water heater. 

Step 2: To connect the circulating pump to the water heater, start by attaching line A to the outlet of the circulating pump, which should be provided by the installer. To start the descaling process, first, connect line A to the inlet drain connection on the water heater. Next, fasten line B to the outlet drain connection on the water heater and direct the opposite end of line B into a descaling reservoir.

Finally, connect the inlet side of the circulating pump to line C from the descaling reservoir and install a filter at the end of the line inside the reservoir. To avoid leaks or malfunctions while descaling, it is important to ensure that all connections are tightly and securely fastened.

Step 3: Fill the descaling reservoir with a descaling solution so that both lines inside are submerged. I recommend using a straight white vinegar solution for descaling the heat exchanger. If you choose to use a commercial descaler, make sure to follow the manufacturer’s instructions for the proper dilution ratio.

Step 4: Ensure that both drain connections are open and operate the circulating pump while checking for any leaks. To ensure that the descaling solution is properly circulating through the water heater, it is important to check that the solution is flowing from the descaling reservoir, passing through the heater, and then returning back into the reservoir. 

Step 5: You should continue the descaling process by running the solution through the heater until the solution that is returning back to the descaling reservoir is clear. If needed, you may have to change to a fresh solution during this process. To complete the descaling process, it is important to disconnect all lines and drain all solutions from the heat exchanger. Once the solutions have been drained, it is important to dispose of solutions properly.

Step 6: Close the inlet drain connection and position a container under the outlet drain connection. Now you should connect the cold water supply and open the cold water shutoff valve. Next, flush the heat exchanger with clean water to ensure that any remaining descaling solution is removed.

Step 7: Finally, close the cold water shutoff valve, and reconnect the hot water supply to the water heater. Close the outlet drain connection. Connect the electrical supply back to the Bosch tankless water heater. Open the water shutoff valves. Put the unit back in service.

connect the electrical supply back to bosch tankless water heater

How To Drain Bosch Tankless Water Heater?

Draining a Bosch tankless water heater is an important maintenance task that should be done at least once a year. Here are the steps to drain a Bosch tankless water heater:

Step 1: Turn off the power source to the water heater. It is important to turn off the dedicated circuit breaker first.

Step 2: Additionally, to prevent any water flow into or out of the heater during the task, all three water valves connected to the unit should be closed. the blue valve for cold water, the red valve for hot water, and the main valve that supplies water to the entire house. By doing so, you can ensure that the unit is properly shut off and avoid any potential accidents or damage.

Step 3: Release any pressure inside the purge valves on the cold and hot water valves by removing the purge port valve caps. Attach hosing lines to each water valve, making sure to use the appropriate length and follow any manufacturer’s instructions.

Step 4: To open the purge port valves for your equipment, you need to rotate the “T-shaped” handles perpendicular to the position of the hot and cold valves. Clean the tankless water heater with 2.5 gallons of undiluted white vinegar. Avoid using chemical cleaners as they may be harmful to your health.

Step 5: To flush and drain the water heater, it is important to follow the instructions provided by the manufacturer, which may take up to 45 minutes. After completing the flushing process, the purge port valves should be closed by twisting the “T-shaped” handles. Next, the hosing lines should be removed from each water valve and disconnected. 

Step 6: Take care not to break the rubber sealing discs inside, and replace the purge port valve caps. Restart the water heater following the manual’s instructions. Allow water to pass through the pipes by slowly turning on the hot water tap in a nearby sink, which may take two to three minutes for the water to run without air in the mix.

How To Winterize The Unit For Seasonal Use?

To ensure optimal performance and prevent damage, it is essential not to install the water heater in an area where it may encounter freezing temperatures. If the heater needs to be placed in such a location, it is imperative to drain all water from the heater to avoid any potential harm.

To winterize your water heater, take the necessary precautions and follow the steps below:

Step 1: To begin the process of shutting down the water heater, start by pressing the ON/OFF switch to turn off the unit and unplugging the power supply cord. This should cause the display to turn blank, indicating that the water heater is no longer active. Next, shut off the gas supply to the water heater to ensure that it is properly shut down.

Step 2: Next, use the shutoff valve provided by the installer to turn off the water supply to the heater. To relieve pressure and drain the plumbing system, you should open the hot water taps. If water continues to flow after 5 minutes, it is important to check for a possible crossover of the hot and cold water pipes and correct it before proceeding. 

Step 3: To disconnect the water pipes from the water heater and remove any remaining water, start by placing a small bucket underneath to catch any drips or leaks. Next, use an air compressor to blow short bursts of air (up to a maximum of 100psi) through the inlet water connection or filter. Continue blowing air through the connection until no water is present coming through the outlet water connection of the heater.

Step 4: Once the water pipes are disconnected and the remaining water is removed, it is important to empty the condensate trap to ensure that any buildup is removed. After emptying the trap, reconnect the water fittings to the water heater. Once these steps are completed, you can return the water heater to service once the risk of freezing has passed.

How To Reset Bosch Tankless Water After Maintenance

The way to reset a Bosch tankless water heater varies based on the specific model. In the case of a gas tankless unit from Bosch, you will need to press and hold the on/off button for an extended period of time to reset the unit. 

However, for a Bosch electric tankless water heater, you will need to press the red reset buttons on each thermal cutout in order to reset it. To learn more, you can read our ultimate guide on how to reset Bosch tankless water heater.


How long will the Bosch tankless water heater last without maintenance?

The lifespan of a Bosch tankless water heater without maintenance may vary but it is generally recommended to have regular maintenance every 1-2 years to ensure the unit’s longevity and optimal performance.

How often do I need to descale my Bosch tankless water heater?

The frequency of descaling a tankless water heater depends on the hardness of the water and the manufacturer’s recommendation. As a general rule, it is recommended to descale the unit every 1-2 years.

What happens if you don’t clean the Bosch tankless water heater?

If you don’t clean a tankless water heater, mineral buildup can occur and lead to reduced efficiency, decreased hot water flow, and potential damage to the unit. It can also lead to increased energy costs and a shorter lifespan of the heater.

How long does it take to descale Bosch tankless water heater?

The time it takes to descale a Bosch tankless water heater can vary depending on the severity of the scale buildup and the specific model of the water heater. In general, it can take anywhere from 30 minutes to a few hours to complete the descaling process.

How often should I service the water valve on my Bosch tankless water heater?

It is recommended to service the water valve every 2-3 years. Regular servicing helps prevent problems caused by sediment or debris accumulation, ensuring smooth operation and optimal performance.

Wrapping Up:

Bosch tankless water heater maintenance is crucial for optimal performance and longevity. Annual maintenance should include inspecting the venting system, cleaning the heat exchanger’s fin coils, and testing the pressure relief valve. Consider periodic descaling and winterizing to ensure efficient and reliable operation for years to come. Follow these tips to keep your water heater in top shape. 

Also, in case you face ignition issues, you can check out our guide on how to fix Bosch tankless water ignition problems. You are welcome there!

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