F26 Vaillant Boiler fault code meaning causes & fixes
Vaillant fault code F26 refers to poor circulation due to the gas stepper motor
This fault code can be applied to 2 models with different meanings. This fault code is applicable to the Ecotec range. It means that the gas valve activated by the gas stepper motor is not working properly.
When a Vaillant boiler starts to show error codes it could mean it is time for a new one, especially when they get to around 10 years old.
Read our guide to new Vaillant boiler prices here for more information.
What does the F26 fault code on my Vaillant boiler mean?
Poor circulation in ecoTEC boilers is the reason your boiler shows the Vaillant F26 fault code caused by the stepper motor connection.
Every boiler has a return and a flow. After heating, the flow is water leaving the boiler. After passing through all pipes and radiators, the water flows around the heating system and then re-enters the boiler via the return tube.
A thermistor is a sensor located on the return pipe. This measures water resistance in response to temperature. The resistance reading will decrease the higher the temperature. The printed circuit board (PCB), converts this resistance reading into a temperature and decides if it is correct.
The thermistor may have noticed a lower return temperature than the flow temperature in this instance. This is because your boiler is not circulating water properly.
The PCB detects when there is a problem and displays a fault code to indicate that it must be fixed. It might even lock out in extreme cases. This prevents any damaged components from becoming more severe.
Can I fix the Vaillant F26 fault code by myself?
The F26 fault code cannot be repaired on a DIY basis. A boiler repair company will need to inspect your appliance. After they have diagnosed the problem and repaired it, they can reset your boiler. Resetting the boiler will remove the F26 fault code.
What causes F26 Vaillant boiler fault to display?
The central heating engineer will have to inspect various components that can affect temperature readings or circulations. This includes your Vaillant boiler as well as your entire central heating system. What will they be looking for?
- The heating return NTC thermometer will give you the correct resistance readings
- The PCB and NTC thermistor are connected and wired
- To ensure that the water is circulating correctly, the pump
- Air locks
- Blockages
Your heating engineer will begin with the NTC thermometers because they can be defective and indicate incorrect temperature readings. This could lead to the PCB believing there is a circulation problem when there isn’t.
How can I have my heating company verify the resistance reading of my NTC thermistor?
The NTC thermistor is what helps the PCB determine the temperature of the water in the heating system. A multi-meter is the best tool to test this component.
They would expect to see resistance readings of approximately 12K ohms at 20C. It’s possible that the NTC thermostat on the heating return is failing if it’s higher or lower than this or if it’s not found at all. A new NTC thermostat will be required in this instance.
What is the Vaillant F26 fault code displayed on my boiler?
Electrical components are very fragile. A component could fail if it sustains even the smallest of damages to wiring or connections.
Water damage is another example. Water damage can cause many Vaillant boilers to fail. A heating pump that has leaking seals can cause enough moisture damage to the components and wiring/connections.
A visual inspection by your heating company is a good way to start. It will look for burnt connections or damage to the wiring.
Many cases of damage are caused by loose connections. These connections can be easily secured. However, damage must be repaired in order for the PCB’s to communicate effectively with the NTC thermometer on the central heating return pipeline.
How is it possible that the pump can cause the Vaillant F26 fault code to be displayed?
The NTC thermistor is not only on the return pipe but also on the flow. The PCB logs the temperature of water leaving the boiler. The same goes for water that is re-entried through the return pipe.
Any circulation restriction can affect the flow and return water temperatures. It takes water longer to travel around the heating system than normal, which will cause it to lose more temperature.
This means that the difference between the two readings of the thermistors is too large, and that the Vaillant boiler locks out.
The heating company will have to verify that the pump is set at the right speed. There are three speeds available on most modern pumps. If the pump is on the lowest speed setting, and your heating system is large, you might need to switch to a higher setting.
They will then need to make sure there are no blockages. This could be caused by a combination or air and heating sludge.
You can remove the air using the bleed screw and the heating oil sludge manually. To ensure that the heating sludge does not return, they will need to flush out the heating system, inject inhibitor and install a boiler filter to trap and collect long-term debris.
A limescale filter is recommended by the heating company. Should I buy one?
Prevention is always better that cure. Limescale is a common problem in areas with hard water. It can cause a blockage of the pump and heat exchanger, which is a costly part to replace.
A limescale filter can reduce the possibility of a pump becoming blocked and other costly components. It will also make your boiler run more efficiently. A limescale filter is a smart investment if you live in hard water areas. Magna Clean is a top brand.
My boiler engineer says I need a new pump. How much is it going to cost?
Pump fault codes and Vaillant F26 fault codes are not all easy to fix. It might be worth looking into a replacement if your pump is acting up due to long-term water damage or worn bearings.
We would expect a replacement pump costing around £260. This is a high-quality pump made by Grundfos and includes labour.
What are the best ways to remove air locks?
As we’ve mentioned, air locks can also occur in pumps and can be removed with the bleed screw. They are most commonly found in radiators and towel rails. They can also be easily removed by DIY.
Before you remove air locks, make sure to check the pressure of your boiler. It should be about 1.3 bars.
Choose a radiator and protect your walls and floors. Make sure to have a container on hand to catch any water that may be released from the radiator.
A radiator bleed key can be used to open the bleed screws. You will hear a hissing sound as air is released from the system. After all the air is released, the hissing sound will be replaced by a dribble water. This means that the radiator has lost all air.
You’ll need to go to the boiler after you have removed all radiators and towel rails. After releasing the air from your system, you will have removed pressure. You will need to add pressure if the pressure drops below 1.3 bars.
How can I increase the pressure in my Vaillant boiler?
The filling loop is a small braided pipe with a valve. This valve will allow water to enter the system. Your Vaillant boiler’s pressure gauge will show an increase in pressure. We are trying to get 1.3 bars.
You can also release excess pressure by squeezing the radiator, as you did before. This time you will need to allow water to escape and have someone check the pressure gauge to tell you when it is at 1.3 bar.
