Safety: Isolate power before accessing the wiring compartment.

Check control settings: Ensure the programmer is set to HEATING ON and the thermostat is turned up.
Test boiler in manual mode: Many Main boilers can be forced into test mode or manual operation via the front panel; consult the manual. If the boiler runs, the internal components are likely fine.
Bypass controls (temporary test): Fit a link across the room thermostat terminals at the boiler. If the boiler now responds, the fault is in the external controls or wiring.
Engineer tasks:
- Trace and repair any breaks in thermostat cable.
- Replace faulty programmer or thermostat.
- Verify correct wiring according to the Main installation diagram.

Boiler does not respond to room thermostat or programmer, but has power and pressure

Possible Causes