BoilerFaultCodesKeston E35 Fault Code
The Keston E35 fault code means: your boiler is struggling to detect a stable electrical signal from the mains power supply, causing it to shut down as a safety precaution.. It appears on 9 Keston models in our database.
Technical description: Mains supply frequency incorrect - There may be a problem with your power supply.
What causes the Keston E35 fault?
This fault occurs when the boiler's internal computer detects that the incoming electricity from your home is not at the steady frequency it requires to operate safely. The most common reason is an issue with the local power grid or faulty electrical wiring within the property that is interfering with the power signal. In some cases, the boiler's main control board may have developed a fault, causing it to misread an otherwise healthy power supply.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Gas Safe Register →Keston models that show the E35 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Keston E35 fault code information on this page is sourced and cross-checked against the official Keston service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026