Thermostat display shows E1 and heating does not start or stops shortly after calling for heat.

Safety first: Turn off power to the thermostat at the circuit breaker or remove the batteries before opening or removing the device from the wall or radiator valve.

Steps to try:

• Power cycle the thermostat: Remove batteries (for Ally radiator thermostat) or turn off the power (for wall thermostat), wait 2–3 minutes, then restore power. Check if E1 clears.
• Check ambient conditions: Extremely high humidity or condensation on the thermostat can cause sensor errors. Wipe the housing dry and allow it to acclimate to room temperature for 30 minutes, then test again.
• Inspect mounting: Ensure the thermostat is not installed directly above a heat source (radiator, TV, lamp) or in direct sunlight, which can overheat the internal sensor and trigger a fault. Relocate the wall thermostat if necessary.
• Factory reset: Follow the Danfoss Ally manual to perform a factory reset on the thermostat. Rejoin it to the Ally Gateway and test operation.
• If E1 persists: The internal NTC sensor or main PCB is likely defective. The unit is not field‑repairable; replace the thermostat head or wall unit with a compatible Danfoss Ally model.