E.04-.01 Boiler Fault Code: What It Means on Every Brand

The E.04-.01 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-.01 means	Severity	DIY?
BBaxi	The E.04-.01 code tells you that the boiler's flow temperature sensor — a small NTC thermistor that monitors how hot the water leaving the heat exchanger is — has developed a short circuit. Full guide →	Lockout — engineer likely	No
RRemehashown as E.04.01	The E.04.01 code — shown as E04 on older Remeha Avanta displays — means the boiler has entered an ignition lockout. Full guide →	Lockout — engineer likely	No

E.04-.01 brand by brand

Baxi E.04-.01

The E.04-.01 code tells you that the boiler's flow temperature sensor — a small NTC thermistor that monitors how hot the water leaving the heat exchanger is — has developed a short circuit. In a short-circuit condition, the sensor's electrical resistance drops to near zero, which makes the PCB believe the water is dangerously overheated. As a safety response, the boiler shuts down completely and locks out. Because this is classed as a permanent locking fault, the boiler will not restart by itself; it needs the underlying problem fixed before a reset will hold. Note the two closely related codes: E.04-.02 indicates the same sensor has gone open-circuit (disconnected or broken wire), and E.04-.03 signals that the maximum flow temperature has actually been exceeded or the sensor has short-circuited under a high-temperature condition.

Causes, fixes & costs for Baxi E.04-.01 → · All Baxi codes

Remeha E.04.01

The E.04.01 code — shown as E04 on older Remeha Avanta displays — means the boiler has entered an ignition lockout. It fires this fault after five consecutive failed start attempts without detecting a stable flame. At that point the boiler shuts itself down and holds in a safe state until the problem is resolved or the unit is reset. The root cause falls into one of three broad categories: no spark being produced, a spark occurring but no flame forming, or a flame establishing briefly but the ionisation signal being too weak for the control board to trust it. Because unburnt gas is involved, the boiler is right to lock out rather than keep trying.

Causes, fixes & costs for Remeha E.04.01 → · All Remeha codes

Frequently asked questions

Is the E.04-.01 fault code the same on every boiler?

Broadly, yes — on Baxi and Remeha the E.04-.01 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-.01 fault myself?

Not usually. On every brand listed, E.04-.01 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-.01 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.