Furnace attempts to start but shuts down due to overtemperature, display shows overheat alarm

Safety: Turn off electrical power. Allow the furnace and connected pipework to cool fully before touching any components.

• Check system circulation: Ensure all isolation valves on the flow and return of the Hoval furnace are open. Verify that radiators or air handlers are not isolated.
• Inspect circulation pump: Locate the Hoval-specified circulation pump. Listen for operation when the unit calls for heat. If silent, check the pump fuse and wiring. Gently free a stuck rotor by removing the pump head and turning the shaft with a screwdriver (if design allows).
• Clean heat exchanger: Remove the combustion chamber cover and inspect the primary heat exchanger surfaces for soot or scale. Carefully brush and vacuum according to Hoval service instructions. Do not damage fins or gaskets.
• Reset safety thermostat: Locate the manual-reset safety temperature limiter (often on the flow pipe or heat exchanger). Press the reset button if present. If it trips again, do not bypass it; find and correct the cause.
• Bleed air: Bleed air from high points and automatic air vents in the system to restore proper circulation.

If the overheat condition persists, contact a qualified Hoval service partner to check system design and sensor calibration.