Is your Vaillant boiler displaying the F25 fault code? Here we explain the most common causes and potential fixes.
Each Vaillant boiler model features built-in fault codes. This is the same with most boiler brands on the market.
The purpose of a fault code is to inform you when there is a problem with your boiler while also communicating what the nature of the issue.
You can determine what any given error code means by checking your Vaillant manual.
Some of these errors you could solve yourself, but most fixes require the help of a professional.
But, what about the Vaillant F25 fault code, in particular?
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What Does F25 Mean?
The F25 fault code means that your boiler’s flow temperature has shot up too quickly.
An F25 error will trigger if the flow temperature rises by five degrees per second during a boiler operation.
When this happens, the temperature goes up too fast while the system pressure becomes too low. The F25 error will shut off your boiler for safety reasons (i.e., boiler lockout).
What causes the boiler flow temperature to rise too suddenly?
There are a few potential causes of an F25 Vaillant boiler error.
Here are the probable explanations:
Blockage in the boiler or elsewhere in your heating system.
Airlock in the boiler or elsewhere in your heating system.
The limiter has broken in your boiler.
Your flue thermostat is suffering from an interruption.
The flow and return thermistors have lost calibration.
Can I Fix an F25 Error Myself?
Unfortunately, you can’t address an F25 DIY, at least not fully.
If you want to address a potential blockage or airlock in your heating system, including in your boiler, you can bleed and flush your radiators DIY.
You should also bleed and flush any towel rails you have. However, the final fixes will require a professional either way.
Here is how to bleed your radiators.
Make sure the heating is off. Your radiators need to be cold before you start.
Put a towel and basin under the bleed valve of the first radiator you want to bleed.
Insert the bleed key into the valve.
Turn it counterclockwise, slowly.
You should hear a hissing noise while air begins to escape.
As the water starts exiting via the bleed valve, you must turn the key clockwise, back to its original position. This will close the valve.
Repeat this step for all other radiators.
You may have to perform a boiler reset in order for the error code to vanish.
Moreover, if the problem comes down to faulty part(s) or some other type of boiler malfunction, you’ll need a heating engineer to undertake all the work.
It is unsafe and illegal to deal with most boiler fixes DIY. If in any doubt check your Vaillant manual or/and contact a professional.
Is your Vaillant boiler experiencing some of the brand's most common fault codes? We have covered many Vaillant boiler error codes in the following guides:
Cost of Hiring a Heating Engineer to Fix an F25
The average labour cost of hiring a Gas Safe Register engineer is £30 to £60 per hour. However, it would depend on factors like where you live.
Here is what they would likely charge for specific fixes:
Bleeding 5-10 radiators - £150 to £400.
Bleeding 10-20 radiators - £80 to £120.
Repairing an F25 after you’ve bled your radiators - £30 to £120.
Replacing a limiter - £40 to £80.
Fixing or repairing the flue thermostat - £130 to £380.
Recalibrating or replacing the flow and return thermistors - £150 to £250.
If there is a physical fault with your boiler, particularly in relation to the flue thermostat or flow and return thermistors, you may decide it’s a good time to replace your boiler.
That is, if your boiler is old and you’re looking at spending hundreds of pounds on a repair, it could make sense to simply get a new boiler.
Of course, in these trying times, that may seem unthinkable for many homeowners right now.
After all, the average boiler replacement costs somewhere in the region of £800 to £2,800.
However, the good news is that it’s possible to have a boiler replaced on finance. In other words, you can purchase your new boiler now, but pay later.
Contact us if you have any questions about an F25 error or a related issue with your Vaillant boiler.
You may be interested in Gas Engineer Allen Hart explaining the most common boiler problems and how you can resolve them in the video below:
Will my Warranty Cover Repairs or Replacement Work for an F25 Fault?
Vaillant boiler warranties do not apply unless the repair/replacement job relates to a boiler defect that your manufacturer caused.
As a result, in the majority of cases, an F25 fault repair would not be covered by a warranty.
In addition, even if a repair relates to a manufacturer error, you must ensure your warranty is currently valid.
Vaillant boiler warranties differ depending on the model.
For example, the ecoTEC Pro models have a two-year standard guarantee, while the ecoTEC Plus range comes with a five-year standard guarantee.
All that said, each of these options (and other Vaillant ranges) come with a seven-year guarantee if your boiler is fitted by an advanced installer.
If you have any doubts about the status of your boiler warranty, contact Vaillant. Moreover, specific Ts and Cs also apply to these warranties.
A domestic Vaillant boiler comes with the following Ts and Cs in order for you to have a valid warranty:
Your boiler must be serviced annually by a Gas Safe Registered engineer.
The boiler must have been commissioned within six months of despatch by a Gas Safe Register engineer.
As you can see, it’s pretty unlikely that your warranty will cover a specific repair or replacement job for your Vaillant boiler where an F25 error is a culprit.
Indeed, this is the same regardless of the error code.
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