Grant No Call for Heat or Internal Interlock

Boiler will not start at all, but power is present and display is lit; no burner or fan activity.

Safety Warning

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

Possible Causes

Programmer off or in standby, Room thermostat not calling, Open safety interlock (e.g., low water, overheat), Faulty wiring to boiler demand terminals

How to Fix / Troubleshooting

Safety: None immediate, but do not attempt to bridge safety circuits.

User checks:

Confirm programmer is set to ON or timed period for CH and/or DHW.
Turn the room thermostat up above current room temperature.
Check any external safety devices (e.g., low water cut-off) for reset buttons and reset only if safe and instructed in user manual.

Engineer actions:

Verify a call for heat is present at the Grant boiler’s control terminals.
Trace the control circuit through stats, valves, and wiring centre to find open circuits.
Test internal safety interlocks (overheat, low water) and replace faulty components.

Repair Difficulty

Medium 3/5

Required Part

Room thermostat

Check Price on Amazon

We may earn a commission from links on this page.