Vaillant Boiler F25 Fault – Error Code Guide

The F25 error code affects the Vaillant models ecoTec Pro and ecoTec Plus, and it means that the flow temperature is increasing at too great a rate.

It can be caused by blockages or faulty parts, and a Gas Safe engineer will need to be called out to resolve this issue.

What Does a Vaillant F25 Error Mean?

The Vaillant f25 error code means that the flow temperature has risen too high too fast. 

If the temperature is increasing at 5 degrees per second while the boiler is in operation, this means that the flue temperature is too high, and the system pressure is too low. 

This will cause a safety shut off then this will trigger an F25 error code. 

The F25 also triggers a safety shut off, meaning your boiler will turn off until the error is resolved.

What Causes a Vaillant F25 Error?

The F25 can be caused by a blockage or airlock in the boiler or elsewhere in the system. 

It can also be caused by the pump not running, causing a system fault due to a lack of water flow.

Alternatively, it could be down to parts issues such as flow and return thermistors being out of calibration, the flue gas thermostat being interrupted or the boiler having a broken limiter.

How to Fix a Vaillant F25 error

If the issue is down to a blockage or airlock then the system and boiler should be bled and may need to be flushed. 

If the problem has been caused by a faulty part, then an engineer will be able to diagnose this issue and either clean or replace the part in question.

Can you Fix a Vaillant F25 Error Yourself?

As ever, in order to eliminate the issue of airlocks you can bleed the boiler and all radiators and towel rails yourself. However, you cannot fix an F25 error yourself. 

This is not an easy error to diagnose or resolve, so you will need to call out an experienced gas safe engineer to fix this problem.

Can I Prevent an F25 Error from Happening?

One action you can take to reduce the chances of the F25 error is to protect your heating system from circulation faults by fitting a scale reducer.

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