F25 Vaillant fault code meaning causes and fixes
The Vaillant ecoTec Pro and ecoTec plus models will show the F25 error code. It means that the flow rate is too high in these Vaillant boilers.
This can be caused either by blockages or defective parts. A Gas Safe engineer will be required to investigate the problem to get your central heating system and hot water back up and running.
Older Vaillant boilers start to show faults and errors more often which can mean hefty repair bills and higher energy bills due to them being less economical.
Read our guide to new Vaillant combi boiler prices here for more information.
What does a Vaillant F25 error mean?
Vaillant f25 errors indicate that the flow temperature has increased too quickly.
If the temperature rises at 5 degrees per minute while the boiler is operating, it means that the flue temperature and system pressure are too low.
This will result in a safety shutoff called a lockout and the Vaillant boiler F25 error code.
Your boiler will also turn off when the F25 is triggered.
What Causes the Vaillant boiler F25 fault code?
The Vaillant F25 fault code can be caused either by a blockage in the boiler, or in any other part of the system such as the primary heat exchanger
You can also have the pump stop running, which could cause a system fault due to a lack of water flow.
Alternatively, it could also be due to parts issues like flow and return thermistors not being calibrated, flue gas thermostats being interrupted, or boilers having a broken limiter.
If the Vaillant f25 error code is showing due to an increase in flue gas temperature difference then we suggest that your get your gas valve and system pressure checked by a Gas safe engineer right away.
How to fix a Vaillant F25 fault code
If there is a blockage or an airlock, the boiler and system should be flushed.
A qualified heating engineer can diagnose the problem if it is caused by a defective part and then either replace or clean the part.
Can you Fix a Vaillant F25 Error Yourself?
You can still bleed your boiler, radiators, and towel rails to get rid of the problem of airlocks. You cannot however fix an F25 error by yourself.
This error is difficult to diagnose and fix. You will need to contact an experienced Gas Safe engineer in order to resolve the problem on your Vaillant boiler.
How can I prevent an F25 error from happening?
You can reduce the chance of Vaillant F25 errors by installing a scale reducer to protect your heating system against circulation faults. This will stop a build-up of central heating sludge and limescale protecting thins like the main heat exchanger.
Does the F25 fault code mean I need a new boiler?
We have access to all the top Gas Safe registered heating engineers and if you have an old Vaillant boiler model that is over 10 years old, it may be time to consider a new boiler. This is mainly due to the fact that old boilers are much less energy efficient, but also that the F25 error code can lead to other error codes, which in turn will mean more costly repairs.
