Thermostat clicks or relay chatters rapidly when calling for heat

Safety first: Isolate power before checking wiring.

Steps:

• In the installer menu, increase the hysteresis or adjust the cycle rate to a value recommended for your heating system (fewer cycles per hour for underfloor heating).
• Check that Live and Neutral connections are tight and that the supply voltage is stable.
• Ensure the thermostat is not controlling a load directly that exceeds its rating; use a wiring centre or contactor if necessary.
• If chatter persists despite correct settings and wiring, the relay or driver circuit may be faulty and the thermostat should be replaced.