Stiebel Eltron Flow Sensor Troubleshooting [A Complete Guide]

The flow sensor plays a crucial role in detecting water flow and regulating the water heater’s operation. Any malfunction on this device can cause various problems with your water heater. 

So, how to perform Stiebel Eltron flow sensor troubleshooting? Here are some common problems with the Steibel Eltron water heater flow sensor- 

  • Clogged flow sensor
  • Damaged O-ring 
  • Broken flow sensor

To fix this issue with Stiebel Eltron, you have to perform troubleshooting by cleaning the flow sensor, replacing the damaged o-ring, and replacing the flow sensor itself. 

Before diving into the problems, let’s discuss which signs require troubleshooting the flow sensor of your Steibel Eltron. 

Faulty Stiebel Eltron Flow Sensor Symptoms

If the flow sensor or any of its components in your Stiebel Eltron is faulty, you will mainly face two symptoms. Here are those. 

stiebel eltron flow sensor troubleshooting

01. No Hot Water Or Lukewarm Water

If the flow sensor is not functioning properly, it can not detect the water flow correctly. As a result, the water heater won’t be activated when necessary and will fail to heat the water properly. 

Due to this reason, if the flow sensor is faulty, you might not get proper hot water from Stiebel Eltron water heater even if the power is on. 

02. Rapid Water Temperature Fluctuation

Sometimes, the water heater might give you hot water even with a faulty flow sensor. However, a defective flow sensor can result in erratic temperature fluctuations.

You may experience that, the hot water is turning cold while using the heater or the cold water is suddenly turning very hot. 

This happens because the flow sensor can’t regulate the water flow and doesn’t understand when the new water enters the system. And the system heats the water randomly.

If you are experiencing any of these two symptoms with your Steibel Eltron water heater, it’s time to troubleshoot the flow sensor. Let’s get into that process. 

Stiebel Eltron Flow Sensor Troubleshooting: Quick Overview

Before getting into the detailed troubleshooting process, here is a quick overview of the problem and its solutions. 

Problem Solution 
Clogged flow sensor Clean the flow sensor 
Damaged O-ringReplace the O-ring
Broken Flow sensor Replace the flow sensor

Stiebel Eltron Flow Sensor Troubleshooting [A Complete Guide]

A Stiebel Eltron flow sensor can malfunction mostly due to three reasons. You have to test them one by one and fix them if required. Let’s get into the troubleshooting process.

Problem 1: Clogged Flow Sensor

Supply water consists of different types of minerals and sediments. Over time, these minerals, and sediments can accumulate inside the flow sensor.

These deposits obstruct the flow path and interfere with the sensor’s ability to accurately measure the water flow rate.

How To Fix:

You have to check and clean the sediment and mineral build-up from the Stiebel Eltron flow sensor. Here’s how to do it. 

Tools required

  • Flat-blade screwdriver
  • Compressed air
  • Adjustable wrench

Step 1: Take Precaution

First, shut off the water supply to the water heater. Also, locate the valve that controls the water flow into the unit and turn it off.

Now you have to switch off the power to the water heater at the circuit breaker. It will ensure your safety during the cleaning process. Also, turn any of the hot water faucets in your home to make sure there is no hot water present in the system. 

Step 2: Access the Flow Sensor 

The flow sensor is located inside the access panel of your Stiebel Eltron water heater. Open the access panel to reach the sensor. The flow sensor looks like the following picture. 

flow sensor of stiebel eltron tankless water heater

Step 3: Free the Flow Sensor 

Disconnect the black wiring connection going from the right side of the flow sensor. The white connector should come up right away when you insert a flat-blade screwdriver into it and pull it up. 

Now, look for a small pin or tab located on top of the flow sensor. Use the flat-blade screwdriver to carefully lift this pin or tab. 

There is a nut that is securing the flow sensor from the bottom. Locate the nut at the bottom part of the sensor. Loosen the nut by turning it counterclockwise. Use an adjustable wrench or pliers to turn it.

Step 4: Remove The Flow Sensor

Once the nut is loose, gently wiggle and lift the flow sensor to remove it from its position. Be cautious not to damage any surrounding components or connections.

Step 5: Check The Flow Sensor For Debris

Check the flow sensor for the build-up of sediment and debris. If you find any, go to the next step. If the flow sensor seems clean, go to the next problem in this troubleshooting process.

Step 6: Clean The Flow Sensor 

Use an air compressor to blow away any dirt, debris, or buildup from the sensor. Direct the air into the flow sensor to dislodge and remove any obstructions. 

After blowing away the dirt buildup, inspect the flow sensor to make sure it is clean and free from any remaining debris.

Now, Rinse the flow sensor with water to further clean it. You can use a gentle stream of water or submerge the sensor in a container of clean water to remove any remaining residue.

Once the flow sensor is thoroughly cleaned, let it dry completely before reinstalling it. 

Step 7: Repositioning The Flow Sensor

After drying the sensor properly, carefully reposition it back into its place within the water heater. Tighten the nut at the bottom of the flow sensor to secure it in place. Ensure it is snug but not over-tightened.

After that, lower the pin or tab at the top of the flow sensor by pressing it down gently with the flat-blade screwdriver. Reconnect the wire connector to the electrical connection on top of the flow sensor. Close the access panel door. 

Step 8: Return The Power Supply

Turn on the water supply to the water heater by opening the valve that controls the flow. Finally, restore the power to the water heater at the circuit breaker. Now, the flow sensor should work properly.

Problem 2: Damaged O-ring

If your flow sensor is not very dirty, or if the flow sensor doesn’t work even after cleaning it, the problem can be the O-ring. 

The O-ring is a rubber gasket that forms a watertight seal between the flow sensor and the water heater’s plumbing. If the O-ring is damaged, it can lead to leaks or improper sealing, which can affect the flow sensor’s performance.

How To Fix:

You have to replace the O-ring if you find it damaged. Here is what you have to do. 

Step 1: Remove The Flow Sensor

To take safety precautions and remove the flow sensor, you have to follow steps 1 through 5 given in the previous problem. 

remove the flow sensor of stiebel eltron tankless water heater

Step 2: Inspect The O-ring

Inspect the O-ring beneath the sensor for any signs of damage including cracks, breaks, or deformation. A damaged O-ring can look flattened, torn, or deteriorated. 

If you notice any damage to the O-ring, it will need to be replaced.

Step 3: Remove The Damaged O-ring

Carefully remove the damaged O-ring using a flat screwdriver or your fingers. If there is any melted residue of rubber that stays in the sensor, you have to scrap it out of the sensor. 

Don’t forget to take note of the size and shape of the existing O-ring for reference when acquiring a replacement.

Step 4: Install The New O-ring

Install the new O-ring by placing it securely in the O-ring groove on the flow sensor. Ensure that the O-ring fits snugly and creates a proper seal when the flow sensor is reattached to the plumbing.

Step 5: Reattach The Sensor & Start The Heater

Reattach the flow sensor to the water heater and reattach the all wiring, pins, and nuts to secure the sensor in place. 

Turn on the power supply to the water heater and see if the heater works properly. 

Problem 3: Broken Flow Sensor

If none of the above solutions work, that means the flow sensor of your Stiebel Eltron itself is damaged. 

How To Fix:

You have to replace the flow sensor to fix this problem. Here’s the Stiebel Eltron flow sensor replacement process. 

Step 1: Get a Compatible Flow Sensor

Contact the manufacturer or a reputable supplier to obtain a replacement flow sensor that is compatible with your Stiebel Eltron water heater model. 

Provide them with the necessary information, such as the water heater’s model number, to ensure you receive the correct replacement part.

Step 2: Remove The Faulty Flow Sensor

Before removing the flow sensor, you have to take some safety precautions. After that, you have to remove certain wirings and nuts. For these procedures, follow steps 1 through 5 given in the first problem. 

Step 3: Install The New Flow Sensor

Install the new flow sensor by aligning it with the mounting slots on the water heater. Then you have to secure the flow sensor in place using the pins and screws.

Reconnect the electrical connections or wiring to the new flow sensor. After that, turn on the heater and check.


What does a flow sensor do on a tankless water heater?

A flow sensor in a tankless water heater detects the flow of water and triggers the heating system to start. When hot water is required, the flow sensor detects the demand for hot water and activates the heating process accordingly.

How to reset the Stiebel Eltron water heater?

To reset your Stiebel Eltron unit, locate the red reset button inside the access panel. Press and hold the reset button for a few seconds until the unit powers off. Release the button and wait for a few moments.

How do I know if my heater is broken?

You will know your water heater is broken when there is no heat production or inconsistent or insufficient heat output. Also, there can be unusual noises or smells, frequent cycling on and off, or a malfunctioning thermostat.


Here goes the complete Stiebel Eltron flow sensor troubleshooting process. I hope after reading this article, you can fix the flow sensor problem and get enough hot water. 

If you are not comfortable fixing the water heater by yourself, please consult a professional plumber. That’s all for now. All the best with your water heater and have a great day! 

Remember to check out this article on Stiebel Eltron water heater tripping problem.

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