E135 Boiler Fault Code: What It Means on Every Brand

The E135 fault code appears on 3 boiler brands — Baxi, Main and Potterton — 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 3 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 E135 means	Severity	DIY?
BBaxi	The E135 fault code on Baxi boilers indicates an internal gas supply interruption, placing the boiler into a safety lockout. Full guide →	Lockout — engineer likely	No
MMain	The E135 code on Main boilers indicates that the boiler has shut itself down — locked out — after detecting a problem with its internal gas supply or after failing to achieve ignition. Full guide →	Lockout — engineer likely	No
PPotterton	The E135 code indicates an internal interruption of the gas supply — meaning the boiler itself has detected that gas is not reaching the burner as expected. Full guide →	Lockout — engineer likely	No

E135 brand by brand

Baxi E135

The E135 fault code on Baxi boilers indicates an internal gas supply interruption, placing the boiler into a safety lockout. Rather than pointing to a problem with your home's gas supply itself, this code signals that something within the boiler's own gas handling or control system has failed — the boiler has detected it cannot safely process gas and has shut itself down as a precaution. On some Baxi models, particularly the GA range, E135 is more specifically associated with a PCB-level error, while on others it may present alongside an ignition lockout. In all cases, the boiler will stop producing heat and hot water until the underlying fault is identified and resolved.

Causes, fixes & costs for Baxi E135 → · All Baxi codes

Main E135

The E135 code on Main boilers indicates that the boiler has shut itself down — locked out — after detecting a problem with its internal gas supply or after failing to achieve ignition. Rather than pointing to an issue with your property's external gas supply, this code suggests something inside the boiler is preventing it from lighting correctly. The boiler enters lockout as a safety precaution to stop any potentially unsafe condition from continuing. Because this code is shared across the wider Baxi group platform, you may see E135 on Main, Baxi, and Potterton boilers — they all use the same underlying fault code system.

Causes, fixes & costs for Main E135 → · All Main codes

Potterton E135

The E135 code indicates an internal interruption of the gas supply — meaning the boiler itself has detected that gas is not reaching the burner as expected. Unlike a straightforward external gas supply failure (such as the meter being off or a supplier outage), E135 points firmly to a fault within the boiler's own components. In practical terms, the boiler has registered that the gas valve was open for a period of time without gas flow being confirmed, or that the valve is not functioning correctly. The boiler responds by entering lockout and shutting down completely, so it will not fire again until the underlying fault is diagnosed, repaired, and the unit is reset by a qualified engineer.

Causes, fixes & costs for Potterton E135 → · All Potterton codes

Frequently asked questions

Is the E135 fault code the same on every boiler?

Broadly, yes — on Baxi, Main and Potterton the E135 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 E135 fault myself?

Not usually. On every brand listed, E135 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 E135 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.