Thermostat shows E16 and fails to control electric underfloor heating load

Safety first: Turn off power at the consumer unit and verify isolation. Electric underfloor heating circuits can carry high current.

Steps:

• Check the total wattage of the electric underfloor heating connected to the thermostat and divide by supply voltage to calculate current. Ensure it does not exceed the thermostat's maximum load (e.g., 16A).
• Inspect wiring at the thermostat for correct connection of load and supply terminals; correct any miswiring.
• Use an insulation resistance tester (by a qualified electrician) to check the heating mat/cable for shorts to earth or between conductors.
• If the load is too high, reconfigure the system to use a contactor or relay box controlled by the thermostat, rather than driving the load directly.
• If wiring and load are correct but E16 persists, the thermostat's output device (triac/relay) may be damaged and the unit should be replaced.