E.04-.03 Boiler Fault Code: What It Means on Every Brand

The E.04-.03 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-.03 means	Severity	DIY?
BBaxi	The E.04-.03 code appears on Baxi boilers when either the flow temperature has climbed above the permitted maximum, causing the boiler to lock out for safety, or the flow temperature… Full guide →	Lockout — engineer likely	No
RRemehashown as E.04.03	The E.04.03 code is a hard lockout triggered when the boiler's flow temperature — the temperature of the water leaving the heat exchanger and heading into your heating system — climbs… Full guide →	Lockout — engineer likely	No

E.04-.03 brand by brand

Baxi E.04-.03

The E.04-.03 code appears on Baxi boilers when either the flow temperature has climbed above the permitted maximum, causing the boiler to lock out for safety, or the flow temperature sensor (NTC thermistor) has short-circuited and is reporting dangerously high temperatures even when none exist. Because the boiler cannot distinguish between a genuine overheat and a sensor failure, it shuts down in both cases. This is classed as a permanent fault — it will not self-clear once triggered and requires the underlying problem to be resolved before the boiler can be reset and returned to normal operation.

Causes, fixes & costs for Baxi E.04-.03 → · All Baxi codes

Remeha E.04.03

The E.04.03 code is a hard lockout triggered when the boiler's flow temperature — the temperature of the water leaving the heat exchanger and heading into your heating system — climbs above its maximum permitted safety value. Rather than continue firing and risk damage, the boiler shuts itself down completely and holds the lockout until the underlying cause is identified and resolved. This is part of Remeha's E.04 category, which covers high-temperature safety trips. The most fundamental reason this happens is that heat is building up inside the boiler faster than the circulating water can carry it away — typically because flow through the system is restricted, absent, or the system pressure is too low to support proper circulation.

Causes, fixes & costs for Remeha E.04.03 → · All Remeha codes

Frequently asked questions

Is the E.04-.03 fault code the same on every boiler?

Broadly, yes — on Baxi and Remeha the E.04-.03 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-.03 fault myself?

Not usually. On every brand listed, E.04-.03 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-.03 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.