Danger: Boiler control terminals may carry mains voltage. Isolate power before working on wiring.

Step 1 – Check operating mode and schedule:
- Ensure thermostat is in HEAT mode and not set to OFF or HOLIDAY.
- Review the schedule to confirm the current time period has a sufficiently high setpoint.
Step 2 – Raise setpoint:
- Increase the set temperature by 3–5°C above room temperature.
- Listen for a relay click and check boiler status.
Step 3 – Verify wiring:
- With power off, confirm that the boiler’s thermostat input is wired to the correct relay terminals on the Protherm thermostat.
- Correct any miswiring according to the installation manual.
Step 4 – Test relay continuity (qualified persons):
- During a call for heat, measure continuity across the relay contacts.
- If the relay does not close, the thermostat output is faulty.
Step 5 – Replace thermostat if relay is defective:
- Install a new Protherm smart thermostat and reconfigure.

Thermostat is powered but does not turn the boiler on even when room temperature is below setpoint.

Possible Causes