E.04-.06 Boiler Fault Code: What It Means on Every Brand

The E.04-.06 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-.06 means	Severity	DIY?
BBaxi	The E.04 fault code on Baxi boilers relates to the flue gas temperature sensor and its safety circuit. Full guide →	Lockout — engineer likely	No
RRemehashown as E.04.06	The Remeha E.04.06 fault code belongs to the E4 ignition/flame failure family. Full guide →	Lockout — engineer likely	No

E.04-.06 brand by brand

Baxi E.04-.06

The E.04 fault code on Baxi boilers relates to the flue gas temperature sensor and its safety circuit. Because the boiler has permanently locked out, it will not restart on its own — a manual reset is required at minimum. The three sub-codes each point to a distinct problem: E.04-.04 and E.04-.05 indicate an electrical fault with the flue NTC thermistor, such as a short-circuit, open-circuit, or a poor wiring connection between the sensor and the PCB. E.04-.06 goes a step further and signals that the flue gas temperature actually reached a critically high level, or that circulation through the heat exchanger has failed, or that the sensor is falsely reporting an overtemperature condition. In all three cases the boiler has shut itself down as a precaution to prevent damage or danger.

Causes, fixes & costs for Baxi E.04-.06 → · All Baxi codes

Remeha E.04.06

The Remeha E.04.06 fault code belongs to the E4 ignition/flame failure family. The '04' group covers all faults related to ignition and flame detection, while the '.06' sub-code narrows this down to a repeated ionisation failure — specifically, the boiler has attempted to light and detected a flame at least once, but the ionisation probe has been unable to confirm a consistently stable flame signal. Remeha's own technical guidance describes this as ionisation failing more than five times within a single heat demand cycle. In plain terms: the boiler is trying to fire, something is preventing a clean, stable flame from being held, and the boiler has locked out as a safety measure. Other E4 sub-codes you may encounter include E.04.01 (no ignition spark detected), E.04.02 (spark present but no flame established), E.04.04 (flame signal lost during normal operation), and E.04.07 (repeated flame loss at burner). If your display shows any of these, the diagnostic approach is similar but the specific component at fault may differ — always quote the full code to your engineer.

Causes, fixes & costs for Remeha E.04.06 → · All Remeha codes

Frequently asked questions

Is the E.04-.06 fault code the same on every boiler?

Broadly, yes — on Baxi and Remeha the E.04-.06 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-.06 fault myself?

Not usually. On every brand listed, E.04-.06 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-.06 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.