E.04-.12 Boiler Fault Code: What It Means on Every Brand

The E.04-.12 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-.12 means	Severity	DIY?
BBaxi	The E.04-.12 code is a permanent safety lockout on Baxi boilers, triggered when the control board detects a flame signal at a time when no flame should be present — or when combustion is… Full guide →	Lockout — engineer likely	No
RRemehashown as E.04.12	The E.04.12 code on a Remeha boiler indicates that the ionisation circuit has registered what appears to be a flame signal before the ignition sequence has even begun — in other words,… Full guide →	Lockout — engineer likely	No

E.04-.12 brand by brand

Baxi E.04-.12

The E.04-.12 code is a permanent safety lockout on Baxi boilers, triggered when the control board detects a flame signal at a time when no flame should be present — or when combustion is behaving erratically. Because the boiler's ionisation circuit is reporting a flame that cannot be accounted for, the appliance shuts itself down immediately as a precaution. Unlike some soft faults that clear on their own, this is a permanent lockout: the boiler will stay off until the root cause is resolved and the fault is manually reset. Typical culprits include a faulty or contaminated flame-sensing electrode, a problem with the gas-air mixing unit (sometimes called a venturi), a defective gas valve, excessively high CO2 in the flue gases due to poor combustion, or in some cases a brief mains voltage fluctuation that confused the control board. Because gas combustion is directly involved, a Gas Safe registered engineer should be contacted promptly once basic homeowner checks have been completed.

Causes, fixes & costs for Baxi E.04-.12 → · All Baxi codes

Remeha E.04.12

The E.04.12 code on a Remeha boiler indicates that the ionisation circuit has registered what appears to be a flame signal before the ignition sequence has even begun — in other words, before the gas valve has been commanded to open. Within Remeha's fault-code structure, the E.04 family covers ignition and flame-detection errors; the .12 sub-code specifically identifies this pre-ignition false flame condition. Because the boiler cannot safely proceed with a burner start if it already 'thinks' a flame is present, it locks out immediately as a precaution. This is a safety-critical fault that requires a Gas Safe registered engineer — do not repeatedly reset and run the boiler.

Causes, fixes & costs for Remeha E.04.12 → · All Remeha codes

Frequently asked questions

Is the E.04-.12 fault code the same on every boiler?

Broadly, yes — on Baxi and Remeha the E.04-.12 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-.12 fault myself?

Not usually. On every brand listed, E.04-.12 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-.12 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.