Boiler does not respond to room thermostat, heating will not come on even though hot water works

Safety first: Isolate power before accessing any wiring or control backplates.

User checks:

• Check the programmer is set to ON or timed mode and not OFF or holiday.
• Turn the room thermostat up to maximum and listen for a click or indicator light.
• If wireless, replace the batteries in the thermostat and ensure the receiver has power.
• Check any zone valve manual levers (near the cylinder or manifold) are not stuck in the closed position.

Professional actions:

• An engineer or electrician can test the thermostat, wiring, and zone valve end switches, and replace faulty components.