E.04-.02 Boiler Fault Code: What It Means on Every Brand

The E.04-.02 fault code appears on 2 boiler brands — Baxi and Remeha — and on all of them it points to the same kind of problem. The details still differ by brand (thresholds, sub-codes, reset procedure), so use the table below to jump to the page for your boiler.

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 E.04-.02 means	Severity	DIY?
BBaxi	The E.04-.02 code is a permanent lockout fault on Baxi boilers, indicating that the flow temperature sensor (an NTC thermistor) is showing an open-circuit condition. Full guide →	Lockout — engineer likely	No
RRemehashown as E.04.02	The E.04.02 code is part of Remeha's E04 ignition fault family, and the .02 sub-code tells you something specific: the igniter is producing a spark, but no stable flame is forming. Full guide →	Lockout — engineer likely	No

E.04-.02 brand by brand

Baxi E.04-.02

The E.04-.02 code is a permanent lockout fault on Baxi boilers, indicating that the flow temperature sensor (an NTC thermistor) is showing an open-circuit condition. In practical terms, the boiler's PCB is receiving no valid signal from the sensor that monitors the temperature of water leaving the heat exchanger. Because the boiler cannot safely regulate its output without this data, it shuts down completely and will not restart until the underlying fault is corrected and a reset is performed. The NTC thermistor works by changing its electrical resistance in proportion to water temperature — as the water gets hotter, resistance drops — and this continuous signal tells the PCB how hard the burner needs to work. An open circuit means that electrical path is broken entirely, either at the sensor itself, somewhere in the wiring, or at the PCB connector.

Causes, fixes & costs for Baxi E.04-.02 → · All Baxi codes

Remeha E.04.02

The E.04.02 code is part of Remeha's E04 ignition fault family, and the .02 sub-code tells you something specific: the igniter is producing a spark, but no stable flame is forming. The boiler has made repeated attempts to light the burner — typically more than five — without success, and has shut itself down as a precaution to prevent unburnt gas accumulating. This is distinct from E.04.01, where no spark is produced at all, and E.04.03, where a flame forms but the ionisation signal is too weak to be recognised. Because gas is being called for but not igniting, the boiler locks out until the root cause is addressed and the unit is reset. This is one of the more frequently seen fault codes on Remeha appliances and, while it can sometimes be cleared with a single reset, it nearly always requires a Gas Safe engineer to resolve properly.

Causes, fixes & costs for Remeha E.04.02 → · All Remeha codes

Frequently asked questions

Is the E.04-.02 fault code the same on every boiler?

Broadly, yes — on Baxi and Remeha the E.04-.02 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 E.04-.02 fault myself?

Not usually. On every brand listed, E.04-.02 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 E.04-.02 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.