Lockout lamp illuminating (Overheat Thermostat) High

Malvern Lockout lamp illuminating (Overheat Thermostat) Fault Code

Also written as LOCKOUTLAMPILLUMINATINGOVERHEATTHERMOSTAT — same fault.

The Malvern Lockout lamp illuminating (Overheat Thermostat) fault code means: your boiler has switched itself off to prevent damage because the unit has become too hot.. It appears on 1 Malvern model in our database.

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description: The overheat thermostat will trip if the water flow rate is insufficient.
Typical repair cost £90-180 (including labour)

DIY fix possible

Check that all radiator valves are fully openEnsure the system pressure is between 1 and 1.5 barWait for the boiler to cool down and gently press the reset button

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Malvern models that show the Lockout lamp illuminating (Overheat Thermostat) fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Malvern Lockout lamp illuminating (Overheat Thermostat) fault code information on this page is sourced and cross-checked against the official Malvern service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026