Display indicates RETURN TEMP LOW; boiler may short-cycle or limit firing rate.

Safety: System water may be hot; use caution.

• 1. Allow warm-up time: On a cold start, it is normal for return temperature to be low. Let the system run and monitor whether the message clears as temperatures rise.
• 2. Check mixing valves: If equipped with a system mixing valve, ensure it is not stuck fully open to the return side.
• 3. Inspect return sensor: Confirm the return temperature sensor is properly attached to the return piping and wired correctly.

If RETURN TEMP LOW persists under normal operation, a technician should evaluate system design and sensor calibration.