Thermostat display shows F1 and heating will not turn on

Safety first: Isolate power to the boiler and thermostat at the fused spur or breaker before removing the thermostat from its backplate. Confirm with a non-contact voltage tester.

Steps to check and fix:

• 1. Inspect the backplate wiring: Remove the Ideal smart thermostat from its wall/backplate. Check the CH call terminal (often marked 'CH ON', 'CALL', or 'NO'). Ensure the conductor is firmly clamped and not broken. Re‑terminate any loose wire and tighten the terminal screw.
• 2. Check cable continuity: At the boiler wiring centre or boiler terminal strip, locate the corresponding CH call wire from the thermostat. With power still off, use a multimeter on continuity mode between the thermostat CH terminal and the boiler CH terminal. If open, the cable is damaged and must be repaired or replaced.
• 3. Inspect the backplate connector pins: Examine the thermostat backplate pins and mating contacts for corrosion, bent pins, or heat damage. Clean lightly with electrical contact cleaner and a soft brush. If pins are damaged, replace the backplate.
• 4. Test the internal relay: With power restored and the thermostat calling for heat, listen for a click from the thermostat. If no click and F1 persists despite good wiring, the internal relay or PCB is likely faulty and the thermostat head should be replaced.
• 5. Reset the thermostat: Power cycle the thermostat by turning off the fused spur for 30 seconds, then back on. Clear the error if prompted and test a heating demand.

When to call a professional: If you are not comfortable testing continuity or the wiring is not clearly labelled, contact a qualified heating engineer or electrician.