Thermostat displays E05 and will not control the heater; may show a warning about load or relay.

Safety first: Turn OFF the breaker and verify power is off before working on wiring. Overcurrent conditions can cause fire risk.

Steps to resolve:

• Confirm heater load rating: Check the wattage and voltage of the connected baseboard or in-floor heater. Calculate current (I = P/V) and ensure it does not exceed the thermostat’s maximum rated amperage.
• Inspect heater circuit: Look for obvious shorts, damaged heater wiring, or burnt connections at junction boxes and heater terminals.
• Check thermostat terminals: With power OFF, remove the thermostat and inspect the LOAD terminals for discoloration, melting, or burnt smell indicating relay/triac damage.
• Test with a smaller known-good load: If possible, temporarily connect the thermostat to a smaller heater within spec to see if E05 clears. If it still shows E05, the internal relay/triac is likely damaged.

If the heater load is within spec and wiring is sound but E05 persists, the output stage (solid-state relay/triac) on the main board has likely failed. Replace the thermostat and correct any overload conditions before powering up.