E6 error and thermostat does not switch the boiler or underfloor heating relay; no heat demand is sent.

Safety first: Turn off power to the heating system and thermostat at the main breaker before opening any wiring compartment. Verify with a non‑contact voltage tester.

Steps:

• Check wiring against diagram: Remove the thermostat from its base and compare the wiring to the Danfoss Ally installation manual. Ensure live, neutral, and switched live (or dry contact) are in the correct terminals.
• Inspect for damage: Look for burnt insulation, discoloration, or melted plastic around the relay terminals. If present, the thermostat must be replaced.
• Measure load: Confirm that the connected boiler or actuator load does not exceed the rated switching current of the Ally thermostat relay. If it does, an external contactor should be used.
• Test relay function: With power restored and covers in place, call for heat and listen for a relay click. If E6 appears and no click is heard, the relay is likely defective.
• Replace unit: Danfoss Ally thermostats are not designed for relay replacement in the field. Replace the complete thermostat and correct any wiring or load issues before reconnecting.