Smell gas? Leave the property and call the National Gas Emergency line on 0800 111 999

F.27

Vaillant fault code

Vaillant F.27: A flame signal was detected while the burner should be off

Engineer only

The boiler is sensing a flame when there shouldn't be one. Vaillant's fault table points to a defective flame detector.

What you can safely do

There is nothing you can safely do yourself with this one. Leave the boiler off and book an engineer.

Find a Gas Safe engineer near you Opens the official Gas Safe Register search.

Applies to: ecoTEC plus. Codes can differ between models, so check your manual.

From Vaillant's own fault tables. Your model name is usually on the front of the boiler or in the user manual.

Model	Meaning	Causes listed for engineers
ecoTEC plus	Safety switch-off: flame simulation	Moisture on the electronics, flame monitor electronics defective, gas solenoid valve leaking

Can I reset F.27?

Don't keep resetting it. The flame detection needs checking by an engineer.