F2 displayed, furnace attempts ignition but shuts down after a few seconds

Safety first: Turn off power and close the gas valve. Do not attempt gas pressure adjustments unless you are licensed.

• Step 1 – Check gas supply basics: Confirm that the main gas cock is fully open and that other gas appliances in the home operate normally. If gas supply is intermittent, contact your gas provider.
• Step 2 – Inspect burner and injectors: Remove the burner access panel. Visually inspect the main burner and injector rail for dust, rust flakes, or spider webs. Use a soft brush and vacuum to clean. Do not enlarge injector orifices.
• Step 3 – Check condensate and flue: On condensing Protherm furnaces, a blocked condensate trap or flue can disturb combustion. Verify that the condensate trap and hoses are clear and that the flue terminal is not obstructed by ice, leaves, or nests.
• Step 4 – Observe ignition sequence: Restore power and gas, then reset the unit. Watch through the inspection window: if the flame lights strongly then drops out, the gas valve modulation or flame sensing may be unstable.
• Step 5 – Technician tasks: A certified technician should measure inlet and burner gas pressures, verify combustion with an analyzer, and test the Protherm gas valve coil resistance. If the valve or PCB modulation output is faulty, they must replace and re‑commission the system.