FA Boiler Fault Code: What It Means on Every Brand

FA is a 'flame detected when it should not be' fault on Worcester Bosch — the ionisation circuit sees a flame with the gas valve shut, which the boiler treats as a serious safety condition — and a reversed flow-and-return warning on Ideal. The Worcester version should never be reset repeatedly.

Lockout — engineer likely 2 brands use this code

Which brand is your boiler?

The brand is printed on the front casing. Tap your brand for the full causes, fixes and repair costs.

Brand	What FA means	Severity	DIY?
IIdeal	The FA fault code on Ideal boilers indicates that the boiler has detected a reversed flow and return condition. Full guide →	Lockout — engineer likely	No
WBWorcester Bosch	The FA fault code means your Worcester Bosch boiler has detected a flame signal at a point when the gas valve should be fully closed and no combustion should be taking place. Full guide →	Lockout — engineer likely	No

FA brand by brand

Ideal FA

The FA fault code on Ideal boilers indicates that the boiler has detected a reversed flow and return condition. In a correctly plumbed system, hot water leaves the boiler via the flow pipe and returns to be reheated via the return pipe. When the boiler's sensors detect that water temperatures suggest these are the wrong way round — most often because the circulation pump is pushing water in the wrong direction — the PCB triggers a safety lockout and displays FA. The boiler will not fire until the underlying problem is identified and corrected, and the fault is manually cleared.

Causes, fixes & costs for Ideal FA → · All Ideal codes

Worcester Bosch FA

The FA fault code means your Worcester Bosch boiler has detected a flame signal at a point when the gas valve should be fully closed and no combustion should be taking place. In plain terms, the boiler's ionisation circuit is picking up what it believes to be an active flame after the burner has been instructed to stop — a situation the boiler treats as a potential safety hazard and responds to by locking out. Two sub-codes are commonly displayed alongside FA: FA 306 indicates a persistent false flame signal after the burner has shut down, while FA 364 points to a leak-test failure on gas valve solenoid EV2 (a closely related code, FB 365, flags the same failure on solenoid EV1). All three variants share the same underlying concern — unintended gas or flame activity — and should be treated with the same level of urgency. This fault is the opposite of the EA code (no flame detected during ignition); FA is arguably the more serious of the two because it suggests gas may be passing through the valve when it should not be.

Causes, fixes & costs for Worcester Bosch FA → · All Worcester Bosch codes

Frequently asked questions

Is the FA fault code the same on every boiler?

Broadly, yes — on Ideal and Worcester Bosch the FA code points to the same class of fault, and the recommended response is similar. Model-specific details such as sub-codes and reset procedures still vary, so follow the page for your own brand.

Can I fix a FA fault myself?

Not usually. On every brand listed, FA points to a fault that needs a suitably registered engineer to diagnose and repair. A single reset to rule out a transient glitch is reasonable; repeated resets are not.

Who should I call about a FA fault?

For gas boilers, a Gas Safe registered engineer — it is a legal requirement for any work on the appliance. If you smell gas at any point, leave the property and call the National Gas Emergency line on 0800 111 999.

General guidance only — not a substitute for professional advice, and not certified by a registered engineer. Any work on a gas appliance must be carried out by a Gas Safe registered engineer. If you smell gas, call 0800 111 999.