Boiler shuts down with an overheat indication, manual reset overheat thermostat has tripped on the front or top of the boiler casing.

Safety: Turn off power and allow the boiler to cool completely before attempting a reset. Never bypass an overheat thermostat.

User actions:

• Check the system pressure on the gauge; if low, top up via the filling loop to the recommended cold pressure.
• Ensure all radiator and isolation valves around the Grant boiler are open to allow circulation.
• Once cool, press the manual reset button on the overheat thermostat (usually a small red button). If it trips again, do not continue resetting.

Engineer checks:

• Confirm the circulating pump (e.g., Grundfos or Wilo fitted in Grant system) is running and not seized; replace if noisy or not spinning.
• Bleed air from automatic air vents and high points in the system to remove airlocks.
• Inspect and, if necessary, clean or replace the plate heat exchanger and any magnetic system filter for sludge blockage.
• Test the boiler thermostat or NTC sensor for correct resistance values and replace if out of specification.

Persistent overheating indicates a circulation or control fault and must be investigated by a qualified engineer.