Keston E11 Fault Code: Causes, Fixes & Repair Costs
What does the Keston E11 fault code mean?
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.
General guidance only — not a substitute for professional advice, and not certified by a Gas Safe engineer. Always have your specific appliance assessed by a qualified professional. Any gas work must be carried out by a Gas Safe registered engineer. If you smell gas or suspect carbon monoxide, leave the property and call the National Gas Emergency line on 0800 111 999.
Common causes
- Faulty or failing PCB Common
The most frequent culprit. The control board may have suffered a component failure, lost its configuration, or simply reached the end of its reliable service life. On older Keston boilers especially, PCB degradation is a well-known issue that triggers E10, E11, and E12 fault codes.
- Water leak damaging the control board Common
Internal boiler leaks are a leading cause of PCB damage. Water dripping onto or near the control board causes short circuits and corrupts the electronics. If a leak is present, it should always be identified and repaired before any PCB replacement is carried out — otherwise the new board risks the same fate.
- Loose, corroded, or damaged wiring Sometimes
Poor electrical connections between the PCB and other components — such as the fan, gas valve, or sensors — can generate false error signals and trigger an E11 lockout. Wiring can degrade over time or be disturbed during servicing.
- Underlying component fault shutting down the board Sometimes
Occasionally, a separate fault elsewhere in the boiler — such as a failing sensor, fan issue, or ignition problem — generates a signal the PCB cannot process correctly, causing it to throw an E11 as a secondary response rather than the primary failure.
How to fix it
- Power-cycle the boiler DIY safe
Switch the boiler off at the mains isolator or programmer and leave it off for at least 30 seconds. Turn it back on and allow it to complete its startup sequence. A brief power interruption can clear a transient electronic fault. If the E11 reappears immediately, move on to the next step rather than repeating this more than two or three times.
- Press the reset button DIY safe
After a lockout, Keston boilers require a manual reset before they will attempt to fire again. Press and hold the reset button (usually marked with a flame or reset symbol on the front panel) for a few seconds. If the fault clears and the boiler runs normally, monitor it closely over the next day or two. If E11 returns, further investigation by an engineer is needed.
- Check for visible water leaks around the boiler DIY safe
Look around the base of the boiler, the pipework connections, and inside the boiler casing if you can safely see in without removing panels. Any signs of dampness, corrosion staining, or dripping water should be noted and reported to your engineer. Do not attempt to repair a leak yourself — but flagging it early helps the engineer prioritise the correct fix and avoids spending money on a new PCB while a leak remains.
- Arrange a Gas Safe engineer visit for diagnostic testing Gas Safe engineer
An engineer will use a multimeter to confirm whether the PCB is receiving the correct power supply and sending appropriate signals. They will also inspect all wiring harnesses and connectors for damage, corrosion, or loose terminals. This diagnostic work must be carried out by a Gas Safe registered engineer — do not attempt to open the boiler casing or touch any internal components yourself.
- Repair any identified leak before replacing the PCB Gas Safe engineer
If a water leak is found during the engineer's inspection, it should be fixed first. Fitting a new control board into a boiler that still leaks is likely to result in the same E11 fault returning within months. Leak repairs typically involve replacing seals, a heat exchanger, or pipework joints — all Gas Safe work.
- PCB / control box replacement if required Gas Safe engineer
Where the PCB is confirmed faulty and no underlying cause can be resolved, a full control board replacement is required. The engineer will source a compatible unit for your specific Keston model (C36, C40, or C55), fit and configure it, and carry out commissioning checks before returning the boiler to service. On older boilers, it is worth discussing with the engineer whether replacement of the entire boiler may be more cost-effective than a PCB at this stage.
Parts you may need
- PCB / Control Board (model-specific) · from £280
- Wiring Loom / Harness · from £45
- Ignition Control Module (C36 where ignition-related) · from £95
The exact spare depends on your boiler's GC number (on the data badge). Check this against the part before buying.
Typical repair cost
Expect to pay roughly £150–£500, depending on the underlying cause.
Frequently asked questions
Can I fix the Keston E11 fault myself?
The only safe DIY actions are a power-cycle and a boiler reset. Everything beyond that — testing the PCB, inspecting internal wiring, repairing leaks, or replacing the control board — must be carried out by a Gas Safe registered engineer. Working on boiler electronics without the correct qualifications is unsafe and could invalidate your boiler warranty or home insurance.
How much does a Keston PCB replacement cost in the UK?
A full PCB replacement on a Keston boiler typically costs in the region of £400–£550 once parts and labour are included, with the board itself accounting for the majority of that figure. However, if the underlying problem turns out to be a wiring fault or a repairable component, your bill could be considerably lower — closer to £150–£250 for diagnosis and repair. Always ask the engineer to carry out a full diagnostic before committing to a new board.
My Keston C36 shows E11 — is it a PCB fault or an ignition fault?
On the C36, E11 is primarily listed as a control box error, but certain firmware versions of the C36 also associate E11 with ignition failure. In practice, an engineer will test both the PCB and the ignition circuit during their diagnosis. The two are related — ignition problems can produce signals the PCB cannot process, triggering an electronics fault code — so both systems will typically be checked at the same visit.
Is it worth repairing a Keston boiler with an E11 fault, or should I replace it?
This depends heavily on the boiler's age and service history. If the boiler is under 10 years old and has been regularly serviced, a PCB repair or replacement is usually worthwhile. On older Keston models — particularly the Qudos range — efficiency is significantly lower than modern alternatives, and a PCB replacement costing £400–£550 on top of an ageing boiler may not represent good value. Ask your engineer for an honest assessment before proceeding.