Burner does not start, display indicates overtemperature or safety limit trip

Safety: Allow the furnace to cool completely. Turn off power before removing any covers.

Steps:

• Check system circulation: Ensure that all heating zone valves are open and that the circulation pump (if present) is running when there is a call for heat. Listen for pump operation or feel for vibration.
• Inspect air filters and ducts (warm air furnace): Replace clogged air filters and ensure supply/return grilles are not blocked.
• Reset high-limit thermostat: Locate the manual reset high-limit on the furnace or boiler body (often a red button). Press firmly until it clicks. If it trips again, do not continue resetting—there is an underlying overheating problem.
• Check flue and heat exchanger: Visually inspect for obvious blockages in the flue path. Do not dismantle sealed combustion components unless qualified.

If E05 recurs, contact a Weishaupt service technician to inspect the heat exchanger, circulation system, and temperature sensors.