Error F3

Safety precautions:

1) If the boiler is displaying F3, do not attempt to run heating or hot water until the fault is cleared and a safe condition is confirmed. 2) If you smell gas, evacuate the property and call the gas emergency service immediately. 3) Isolate mains electricity to the boiler and/or switch off at the isolator only when instructed or if you will remove the outer casing — do not open the casing unless you are Gas Safe qualified.

Initial homeowner checks (safe, non-invasive):

1) Note the exact fault display and whether it is constant or intermittent. 2) Try a simple reset: switch the boiler off at the programmer/boiler, wait 1–2 minutes, then switch back on and see if F3 returns. A temporary reset can indicate intermittent fault but does not replace a proper diagnosis. 3) Check the external flue terminal for obvious blockages (leaves, bird nest, debris) from outside the property and clear any external obstruction safely from ground level only. 4) Listen for unusual noises on start-up (grinding, loud bearing noise) which suggest worn or seized bearings. 5) Check around the boiler for signs of leaks or moisture (wet wiring, water on top of the casing). If you find water, turn the boiler off and call an engineer — wet wiring/PCB can be dangerous.

Further diagnostic points (do NOT open or touch internal components unless qualified):

1) If the fault only appears under certain conditions (cold start vs return from thermostat), record the pattern and times to give to the engineer. 2) If the boiler was recently installed or worked on, tell the engineer — incorrect fan speed settings or loose harnesses after install are common causes. 3) Photograph the error code, boiler model/serial, and any visible external flue condition to help the engineer prepare.

What a Gas Safe engineer will do (why you should call a pro):

1) Safely isolate, remove the casing and test fan rotation, current draw and speed with the correct instruments. 2) Inspect and test the fan motor, bearings and impeller for wear/jamming; replace the whole fan assembly if required (bearings alone are usually not replaced). 3) Check the flue path internally and externally for blockages or damage and verify correct flue terminal position and seals. 4) Inspect wiring harnesses and connections between fan and PCB for loose, corroded or water-damaged wiring; dry/replace wiring as required. 5) Test the PCB inputs/outputs to confirm it is registering the fan correctly; replace the PCB only if it is defective. 6) Verify and adjust fan speed settings if they are incorrect or have been altered. 7) After repairs, perform combustion and safety checks, reassemble, clear the fault and run the boiler through several cycles to confirm the fault is resolved.

When to call immediately:

1) If you discover liquid/wet components inside the boiler, any signs of internal leakage, or a persistent F3 that returns after reset. 2) If you hear loud mechanical noise suggesting seized bearings or grinding.

Final notes:

1) Resetting may clear F3 temporarily but does not fix underlying faults; persistent or recurring F3 requires a Gas Safe engineer. 2) Do not attempt to replace the fan, open the casing, or rewire internal components yourself — working on combustion appliances and gas connections is legally restricted to Gas Safe registered engineers and unsafe DIY can cause carbon monoxide risk or fire. 3) Provide the engineer with the boiler model, serial, service history and any observations (noises, wetness, when the fault occurs) to speed diagnosis.