BoilerFaultCodesIdeal 51 Fault Code
The Ideal 51 fault code means: your boiler has successfully lit the small pilot flame, but the main burner is failing to ignite to provide heat or hot water.. 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 internal safety sensors detect that the initial pilot light is burning correctly, but the instruction to open the main gas supply is failing. The most common reason is a mechanical failure within the gas control valve or a faulty solenoid coil that is unable to physically pull open the valve to let gas reach the main burners.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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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.
- Ideal Classic RS manual (PDF)
- Ideal Mexico Super 100FF / 125FF manual (PDF)
- Ideal Mexico Super CF3 40-80 manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026