Stiebel Eltron Water Heater Not Heating [A Complete Guide]

Has your Stiebel Eltron water heater lost its ability to heat up and produce cold water? If so, you’re not alone. Many homeowners are complaining that the heater fails to heat the water as expected. But why does your Stiebel Eltron water heater not heating?

  • Overloading the heater
  • Lack of power supply
  • Improper plumbing
  • Insufficient water flow

These are the most common reasons for the problem. However, aside from that, a dirty aerator, a distant fixture, or a clogged flow sensor can also be the reason. 

Now to fix the issues you’ll have to follow different steps. For example, resetting the heater is the most common solution. But when there’s a lack of power supply, check the wiring and circuit breakers.

For getting the solution to the other problems, keep on reading.

Stiebel Eltron Water Heater Not Heating: Brief Summary

Now I’ll add a table for the reasons and solutions why isn’t the Stiebel Eltron water heater not heating. If you’re a busy person then this quick guide should help you to easily understand the main reason.

Using too many appliances or distant fixturesUse fewer appliances simultaneously. Reset the water heater if needed.
Inadequate size of the water heaterConsider getting a larger water heater or consult a plumber for sizing.
Lack of power supplyCheck and switch on the circuit breakers, Inspect the wiring.
Improper plumbing connectionInspect and correct any incorrect plumbing connections.
Insufficient water flow to activate the unitClean clogged filter screens, faucet aerators, or shower heads.
Clogged or non-spinning flow sensorReplace the flow sensor.
Dirty or clogged aeratorRemove and clean the aerator.
Tripping of safety thermal cut-outReset the safety reset buttons.

Stiebel Eltron Water Heater Not Heating: Detailed Guide

Now it’s time to discuss the problem, Stiebel Eltron Water Heater won’t heat up with proper instruction. But before I proceed forward let me clarify that this guide covers both the tankless and mini-tank Stieble Eltron water heater with no heating problem.

Reason 1: Using too Many Appliances/ The Fixture Is Located Far Away

Let’s start with something very usual, mostly applicable to Stiebel Eltron tankless water heaters. Again, let me remind you it’s mostly not the case of the Stiebel Eltron water heater not heating, rather it’s when the Stiebel Eltron water heater not heating properly. 

If you use too many hot water appliances at the same time, it can make your tankless water heater seem like it’s not heating properly. For example, if you and a guest both try to take hot showers while your child is washing dishes with hot water, it can overload your water heater.

A similar problem can happen when your shower starts hot but then turns cold for a while before the hot water comes back. This can occur if you’re using a fixture that is far away from your water heater or if multiple people in a row want to use hot water.

There might be a little bit of hot water left in the pipes, but it’s usually not enough for a full shower. Once that hot water runs out, you’ll probably get some colder water before the heater has a chance to produce more hot water.

How To Fix:

If this only happens occasionally, try using fewer appliances at the same time. Also, notice if it fixes the problem. But if your water heater still doesn’t heat up or heat up properly, there might be another issue. For example, the water heater might have shut off because it was overloaded. If that’s the case, you can usually fix it by resetting the unit. I’ll discuss that in the subsequent section.

Reason 2: The Heater Isn’t Big Enough

Another possibility is that your tankless water heater isn’t big enough to provide sufficient hot water for your household. When the heater continually gets pressure it can even shut down and won’t heat.

How To Fix:

The solution to this problem is pretty straightforward. If the heater isn’t big enough they might think about getting an additional water heater or replacing your current one with a bigger unit. I suggest asking for a plumber or before purchasing informing the shop mechanic about your daily use of water and getting suggested measurements. 

Reason 3: Lack Of Power Supply

If the Stiebel Eltron Tankless Water Heater is not heating the water, it may be due to a lack of power supply to the unit.

lack of power supply

Typically, the unit will not receive any power if the circuit breakers connected to the water heater are switched off. Again if there is any problem with the wiring it can also happen. And the last reason is there is a problem with the electricity.

How To Fix:

I’ve mentioned 3 possible causes and below learn about the solutions one by one.

If the problem is with the circuit breaker then – 

  1. Locate your circuit breaker box or panel.
  2. Examine all the circuit breakers associated with your water heater.
  3. If they are in the “Off” position, switch them to the “On” position. 

If the problem is with the wiring then check the wiring diagram for the specific model and try to understand where the issue is. Reorganize it, hopefully, the problem will be solved.  

If the unit still does not receive power even after turning on all the circuit breakers and securing the wiring, it indicates a problem with your home’s electrical wiring.

In such a case, contact a certified electrician to professionally inspect your home’s wiring.

Before we get into the next problem, here is a suggested solution guide on Stiebel Eltron water heater not turning on. You’ll find so many things in common, even due to this particular reason you can face the issue as well.

Reason 4: Improper Plumbing

Improper plumbing of the water heater can cause it to stop working or fail to heat the water effectively. For example, if you mistakenly connect the cold water pipe to the hot water outlet or the other way around, you won’t get hot water from the unit.

How To Fix:

This is a very easy task to solve the problem. Just read the steps below.

  • Inspect the plumbing connection to the water heater.
  • Correct the connection if it is incorrect.
  • Ensure that the cold water enters the water heater from the appropriate side, typically the right side.
  • Confirm that the hot water outlet is located on the left side of the unit.

Reason 5: Insufficient Water Flow To Activate The Unit

This problem mostly occurs in the Stiebel Eltron Tempra 24 Plus model. The Stiebel Eltron Tempra 24 Plus model requires a minimum water flow of 0.5 gallons per minute (GPM) to activate the unit and provide hot water.

insufficient water flow to activate the unit

If the water flow does not meet this requirement, the water heater will not function or heat the water.

Well, there are several factors can disrupt the water flow at the unit, including:

  1. Clogging of the filter screen due to debris or scale buildup.
  2. Restriction in the faucet aerator or shower head.
  3. Setting the water flow too low.

How To Fix:

This process is a bit lengthy but not too difficult. Let’s see how to solve the issue.

Step 1: First, check the filter screen and ensure it is free from debris. If needed, clean the filter screen using the following tools:

  1. Needle-nose pliers
  2. Adjustable wrench
  3. Plastic bucket
  4. Rag
  5. Turn off the power to the unit at the circuit breaker.

Step 2: Close both the hot and cold water ball valves on the unit. Then place a plastic bucket under the cold water side fittings to minimize water spills.

close both the hot and cold water ball valves

Step 3: Use an adjustable wrench to disconnect the braided steel hose from the cold water connection.

disconnect the braided steel hose from the cold water connection

Step 4: Remove the filter screen from the cold water inlet using needle-nose pliers.

remove the filter screen from the cold water inlet

Step 5: Clean the filter screen under running water in the sink. Use a brush if necessary to remove any remaining debris.

Step 6: Reinsert the cleaned filter screen into the cold water inlet. Screw the braided steel hose back onto the cold water connection and tighten it using the adjustable wrench.

Step 7: If cleaning the filter screen does not resolve the issue, check the faucet aerator or shower head. Clean the aerator if necessary. This is another long step, I’ve discussed it below. For more check reason 7.

Step 8: Additionally, ensure that you have not set the water flow too low. If required, increase the water flow by turning the flow adjustment screw counterclockwise.

Reason 6: Flow Sensor Is Clogged Or Not Spinning

I’ve already mentioned that if the minimum required water flow is not achieved, the water heater will not operate. Additionally, a clogged or obstructed flow sensor can disrupt the water supply to the unit.

flow sensor is clogged or not spinning

Generally, the flow sensor experiences problems due to the presence of debris and the buildup of scale. And it can restrict its proper functioning.

How To Fix:

In this situation, it is advisable to replace the flow sensor rather than attempt to clear the blockage within the sensor. If you want to learn more about it you can check out our another guide on Stiebel Eltron flow sensor troubleshooting.

Reason 7: Dirty/Clogged Aerator

At times, if the aerator in your faucet or shower head is clogged, it can lower the water flow and prevent the water heater from working or heating properly.

dirty or clogged aerator

How To Fix:

To fix it you’ll have to clean the aerator properly. Here’s a step-by-step guide.

Step 1: The initial step here is to check underneath your sink for the shut-off valves of both the hot and cold water. Ensure that these valves are fully open, as sometimes the issue arises from accidentally closed valves.

Step 2: Now remove the aerator, located at the end. It is crucial to avoid damaging the aerator by using a wrench. Instead, use a silicone or rubber grip jar opener for a secure hold.

Step 3: Apply firm pressure with the jar opener, and if necessary, use your other hand to stabilize the faucet shaft. This technique works well even for stubbornly stuck aerators. Be cautious not to overtighten or damage the aerator during removal.

Step 4: Upon removing the aerator, you may notice accumulated dirt, debris, and hard water stains. Unfortunately, simply rinsing the aerator will not solve the problem. Thorough cleaning is required to fix this.

Step 5: To clean the inside of the aerator effectively, use white vinegar. Do not insert the vinegar directly into the aerator hole. Instead, press your thumb on the bottom of the aerator to push out the internal components.

Step 6: Now, take note of the order in which the pieces come out and set them aside. Pay attention to the screen in the aerator. Holding it up to the light, you should observe a reduced flow due to clogging.

Step 7: Fill a cup with enough white vinegar to cover the parts. Avoid placing the metal part of the aerator into the vinegar at this stage. It is best to clean it separately just before reinstalling it.

Step 8: Rinse off the aerator parts to remove any initial debris, ensuring they are clear of loose dirt and grime.

Step 9: Submerge the aerator parts in the cup of vinegar and let them soak for a duration between 2 and 24 hours. The vinegar will dissolve the built-up deposits and clean the components effectively.

Step 10: During the soaking process, you may notice bubbles and fizzing, indicating that the vinegar is actively cleaning the aerator.

Step 11: After the recommended soaking time, inspect the aerator parts. They should appear significantly cleaner. If necessary, gently scrub them with a toothbrush to ensure thorough cleanliness.

Step 12: Examine the aerator screen again by holding it up to the light. It should now allow better water flow as the clogs have been removed.

Step 13: As a preventative measure, wipe off any debris or residue from the faucet threads using a toothbrush or rag. Opening the faucet without the aerator will help flush out any remaining debris inside.

Step 14: Wipe the inside of the aerator as well before reassembling it. Insert the cleaned components back into the aerator. Make sure to follow the correct order.

Step 15: Now, thread the aerator back onto the faucet. Use the jar opener for a snug but not overly tight connection.

Step 16: Finally, turn on the faucet and observe the improved water flow. With a properly cleaned aerator, you should fix the heater, not a heating issue.

Reason 8: Tripping Of Safety Thermal Cut-Out

The Stiebel Eltron Water Heater incorporates a safety feature known as the safety thermal cut-out or reset buttons.

When the water in the unit gets excessively heated, the safety thermal cut-out is triggered, cutting off power to the water heater. Consequently, your Stiebel Eltron Tankless Water Heater will stop functioning or heating the water.

How To Fix: 

To resolve this issue, it is necessary to reset the safety reset buttons if the safety thermal cut-out has been triggered. Below I’ve discussed the reset process. If you want, check it.

How To Reset The Stiebel Eltron Water Heater

Below I’ve mentioned a few times resetting the Stiebel Eltron water heater can fix the not heating issue. Now let’s see the very basic method to do it. 

how to reset the stiebel eltron water heater

Step 1: First, turn off the power to the water heater at the circuit breaker to avoid any electrical hazards.

Step 2: Locate the front cover of the water heater. Use a screwdriver to carefully unscrew and remove it.

Step 3: Inside the water heater, you will find the reset buttons. These buttons are typically located on the top of the copper heating vessels. If you are unsure about their location, refer to the image provided in Step 4.

Step 4: Take a pencil with an eraser and gently press the reset buttons. If you feel or hear a click when pressing a button with the pencil, it means the reset has been successful.

reset button of stiebel eltron water heater

Step 5: Once you have reset the buttons, securely close the front cover of the water heater.

Step 6: Go back to the circuit breaker and restore power to the unit by turning on all the circuit breakers connected to the water heater.

Well, I’ve already covered a detailed article on resetting the Stiebel Eltron water heater. If you want, check the given link.


Why is my tankless water heater so cold after a few minutes?

Insufficient water pressure is a major factor that can cause a tankless water heater to become cold during a shower after a few minutes.

How long does it take for the tankless water heater to heat up?

Your tankless water heater should heat up within just 15 seconds. However, it’s important to note that you will still need to wait for the hot water to reach your shower head or faucet.

How does a tankless water heater know when to heat?

Within a tankless water heater system, the heating process is initiated when the system detects a demand for hot water. This signal triggers the activation of a burner, which ignites to heat the cold water flowing through an aluminum heat exchanger.

Final Words

That’s everything on – Stiebel Eltron water heater, not heating. By completely reading all the reasons and solutions you should be clear about the actual reason and how to fix it.

As a final tip, regular maintenance of your Stiebel Eltron water heater is essential to ensure optimal performance and prevent potential issues like not heating at all or not properly heating. Follow the manufacturer’s recommended maintenance guidelines, such as flushing the unit periodically, checking for any leaks, and inspecting electrical connections.

That’s all for now, all the best and if you are interested read our other article on complete guidelines on Stiebel Eltron heater keeps tripping.

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