Vaillant F27 Fault Code Explained
Hertfordshire, Bedfordshire & Cambridgeshire
An F27 fault on a Vaillant boiler means the flame sensor is detecting a flame at a point in the cycle when there should not be one.
This is not a fault to reset and carry on with. It needs a Gas Safe engineer.
What F27 actually means
The boiler expects the burner to be out at certain points in its cycle. If the sensor still reports a flame, the boiler cannot tell whether it has a genuine problem with the gas valve or a faulty sensor, so it shuts down and stays down.
Either possibility is treated as serious, because one of them means gas is reaching the burner when the boiler has not asked for it.
What you can safely check yourself
Nothing on this one. There is no homeowner check that helps with F27, and the components involved are inside the appliance. This needs a Gas Safe engineer.
When to stop, and why
What causes it beyond the simple checks
Most commonly a failed flame sensing electrode giving a false reading, or moisture on the electrode. Less commonly, a gas valve that is not closing properly, which is the reason this fault is treated seriously.
How Vantage can help
We are Gas Safe registered and cover Hertfordshire, Bedfordshire and Cambridgeshire, with an emergency line answered 24 hours a day.
Call us on 01462 506374. See also boiler repair and Vaillant boiler installation.
Frequently asked questions
Can I use my boiler with F27 showing?
No. Turn it off and call an engineer.
Is F27 dangerous?
The lockout is the boiler being safe. The reason it locks out is a fault that needs diagnosing rather than clearing.
Is it usually the sensor?
Often, yes. But it cannot be assumed without testing, which is why it is engineer work.
Related fault codes
Other Vaillant codes: Vaillant F22 · Vaillant F75 · Vaillant F28 · Vaillant F29 · Vaillant F20 · Vaillant F23 · Vaillant F83 · Vaillant F32 · Vaillant F62 · Vaillant F61 · Vaillant F72
The same problem on other makes (ignition and flame faults): Ideal L2 · Ideal F2 · Baxi E133 · Glow-worm F28 · Viessmann F4
See also our guide to boiler not firing up, the full boiler advice section, and boiler repair.
In Vaillant’s own words
Vaillant describes F27 as a flame signal being detected while the burner is off.
That is why it is not a reset-and-carry-on code. The boiler is reporting flame where there should be none, and it needs a Gas Safe engineer to establish whether that is a genuine flame or a faulty signal.
When to call an engineer
If those checks have not cleared it, the next steps are engineer work and the boiler should not be reset repeatedly in the meantime. Call Vantage Plumbing and Heating on 01462 506374. We are Gas Safe registered under 956889, the line is answered by a person at any hour of any day, and you get a price before anyone starts.
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