03 Low

Grant 03 Fault Code

The Grant 03 fault code means: your boiler is currently idle and waiting for a signal from your thermostat or internal settings to tell it that your home needs more heat.. It appears on 1 Grant model in our database.

Monitor it

This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.

Technical description: BOILER WAIT THERMOSTAT: Boiler is in standby awaiting a switched live input signal or boiler temperature to drop below set point.

DIY fix possible

Check your room thermostat is turned up to a temperature higher than the current room temperatureEnsure your heating programmer or central heating timer is set to 'On'Check that any external weather compensation sensors are not faulty or obscured

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Grant models that show the 03 fault code

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

Source

Grant 03 fault code information on this page is sourced and cross-checked against the official Grant service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026