BoilerFaultCodesIdeal 51 Fault Code
The Ideal 51 fault code means: your boiler's pilot light is failing to stay ignited after you try to light it, meaning the main burner cannot start to provide heat.. It appears on 3 Ideal models in our database.
Technical description: PILOT WILL NOT STAY LIT WHEN THE GAS CONTROL VALVE KNOB IS RELEASED
What causes the Ideal 51 fault?
This fault occurs when the boiler's safety mechanism fails to detect a healthy flame, causing it to shut off the gas supply for safety. The most common reason is a worn-out thermocouple that can no longer generate the small electrical current needed to hold the internal gas valve open. It can also be triggered by a faulty overheat thermostat or a blockage in the pilot injector preventing a consistent flame.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Gas Safe Register →Ideal models that show the 51 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Ideal 51 fault code information on this page is sourced and cross-checked against the official Ideal service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026