F25On Vaillant boilers, fault code F.25 means: Flue (exhaust) fault. Do not keep resetting or using the boiler. Switch it off and call a qualified gas engineer. If you smell gas, leave the building and call the gas emergency number.
Can I keep using the boiler?
Do not keep resetting or using the boiler. Switch it off and call a qualified gas engineer. If you smell gas, leave the building and call the gas emergency number.
Common causes
- Blocked or damaged flue
- Faulty fan motor or fan wiring
How to fix it
- Make sure the flue outlet outside isn't blocked (leaves, snow, nests)
- Have a qualified gas engineer inspect the boiler; never open gas or flue parts yourself
Frequently asked questions
What does Vaillant error F.25 mean?
On Vaillant boilers, fault code F.25 means: Flue (exhaust) fault.
How do I fix Vaillant error F.25?
Start with these steps: Make sure the flue outlet outside isn't blocked (leaves, snow, nests); Have a qualified gas engineer inspect the boiler; never open gas or flue parts yourself.
Is it safe to use the boiler with fault F.25?
Severity: High. Do not keep resetting or using the boiler. Switch it off and call a qualified gas engineer. If you smell gas, leave the building and call the gas emergency number.