Furnace shows E8 and stops, often after running for a short time

Safety first: Turn off power and allow the furnace to cool completely before resetting any safety devices. Risk of burns.

• Check system valves: Ensure that all isolation valves on the flow and return pipes near the furnace are fully open.
• Verify pump operation: Confirm that the circulation pump runs when there is a heat demand. If not, check its power supply and replace the pump if seized.
• Reset safety thermostat: Some Remeha models have a manual reset button on the safety temperature limiter. Once cooled, press the reset button according to the service manual.
• Inspect for scale or sludge: If the system is old or untreated, the heat exchanger may be partially blocked. This requires professional cleaning or replacement.
• Do not bypass safety: Never bridge or bypass the safety thermostat. If it trips repeatedly, call a qualified technician to diagnose the root cause.