Thermostat fails to control electric underfloor heating; floor remains cold.

Safety: Underfloor heating circuits may be at mains voltage. Turn off power at the breaker and verify with a tester before working. If you are not qualified, contact an electrician.

Steps:

• Verify in the installer menu that the output type is set correctly for electric underfloor heating (on/off relay or triac) and that the load rating is not exceeded.
• Inspect the wiring from the thermostat to the heating mat junction box; ensure all connections are tight and correctly terminated.
• Check any external thermal cutout or safety thermostat in the circuit; reset or replace if tripped or faulty.
• With appropriate test equipment and qualifications, measure continuity of the heating mat or cable; an open circuit indicates a damaged heating element that must be replaced.
• If the heating element is intact but the thermostat output never energizes under a heat call, the internal relay/triac may be defective; replace the thermostat.