E11 Boiler Fault Code: What It Means on Every Brand

The E11 fault code appears on 3 brands — Keston, Remeha and Warmflow — and it does not mean the same thing on each. The same two or three characters can signal a pressure problem on one boiler and an ignition fault on another, so identify your brand first and use the table below to jump to the right page.

Up to: Lockout — engineer likely 3 brands use this code Meaning differs by brand

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 E11 means	Severity	DIY?
KKeston	The E11 code indicates that your Keston boiler's control board has detected an internal electronics fault. Full guide →	Lockout — engineer likely	No
RRemeha	The E11 code appears when the boiler's airbox temperature sensor registers readings above the safe operating threshold. Full guide →	Lockout — engineer likely	No
WWarmflow	The E11 code on a Warmflow Agentis combination boiler indicates that the internal thermal store or hot water tank has exceeded its safe upper temperature limit. Full guide →	Lockout — engineer likely	No

E11 brand by brand

Keston E11

The E11 code indicates that your Keston boiler's control board has detected an internal electronics fault. In plain terms, the PCB (printed circuit board) — the brain of the boiler — has either lost its stored settings, encountered a component-level failure, or is struggling to send and receive signals correctly. On C40 and C55 models, the manufacturer describes this as an internal electronics error requiring a reset or control box replacement. On the C36, E11 (alongside the closely related E10) points to a control box fault, though some C36 firmware versions may also associate E11 with an ignition failure — both ultimately trace back to the control electronics. The boiler will lock out and stop operating until the fault is resolved and a manual reset is performed.

Causes, fixes & costs for Keston E11 → · All Keston codes

Remeha E11

The E11 code appears when the boiler's airbox temperature sensor registers readings above the safe operating threshold. In plain terms, the boiler has detected that hot combustion gases are escaping from the heat exchanger into the surrounding airbox area rather than following their intended exhaust path. This is most commonly caused by a breakdown in the sealing between the heat exchanger and the airbox — typically at the viewing glass or the heat exchanger front plate gasket. When the fault triggers, the boiler shuts down to protect itself and will not resume normal operation until the underlying cause is addressed. Note: on some newer Remeha models (such as certain Quinta Ace variants), E11 can alternatively indicate a domestic hot water flow detection fault, where the boiler locks out specifically during a hot water demand. If your boiler is locking out only when hot water is called for, mention this to your engineer as it may point to a flow sensor issue rather than an airbox seal problem.

Causes, fixes & costs for Remeha E11 → · All Remeha codes

Warmflow E11

The E11 code on a Warmflow Agentis combination boiler indicates that the internal thermal store or hot water tank has exceeded its safe upper temperature limit. When this threshold is breached, the boiler's safety system triggers a lockout to prevent damage or danger. The specific component responsible for detecting and acting on this over-temperature condition is the combination boiler Tank Limit Thermostat (Warmflow part 5318). Unlike the separate High Limit Thermostat (part 5223), this device monitors the tank section of the combi unit specifically. Because E11 is a safety lockout rather than a soft warning, the boiler will not resume normal operation until the fault has been properly addressed. Note that Warmflow is an oil-fired boiler brand, so any professional work must be carried out by an OFTEC-registered engineer rather than a Gas Safe engineer.

Causes, fixes & costs for Warmflow E11 → · All Warmflow codes

Frequently asked questions

Is the E11 fault code the same on every boiler?

No. E11 means different things on different brands — see the table above. Always identify your boiler's brand (it is printed on the front casing) before acting on any advice about the code.

Can I fix a E11 fault myself?

Not usually. On every brand listed, E11 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 E11 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.