Furnace displays F20, heating stops, pump may continue running

Safety first: Turn off power and gas. Allow the appliance to cool before touching pipework.

• Check system pressure: Ensure the pressure is within the recommended range. Low pressure can reduce flow and cause overheating.
• Open valves: Confirm that all isolation valves near the furnace and key radiator valves are open to allow adequate circulation.
• Clean filters: If your Saunier Duval system has a return filter or magnetic filter, isolate and clean it to restore flow.
• Inspect pump: Listen for pump operation. If it is noisy, hot, or not running, it may be failing. A technician can test and replace the pump head or complete pump assembly.
• Descale heat exchanger: In hard water areas, the primary heat exchanger can become restricted. Professional chemical cleaning or replacement may be required.