Error F3

Safety precautions:

1. If the boiler has not already locked out, switch it off at the programmer/room thermostat and isolate electrical power at the fused spur or consumer unit; if you suspect a gas smell or a serious leak, turn off the gas supply at the meter, leave the property and call the emergency gas service.

2. Do not remove the boiler casing or attempt to access internal components unless you are a Gas Safe registered engineer. Internal work can create a dangerous situation and is illegal for unqualified persons.

3. Ventilate the area if you suspect combustion gas. Do not operate the boiler until the fault is resolved.

Initial homeowner checks (safe, non-intrusive steps you can do):

1. Note the error: write down the exact code (F3), boiler make/model and any other displayed messages. Take a photo if helpful for the engineer.

2. Reset the boiler: switch it off at the programmer and the fused spur, wait 2–5 minutes, then switch back on and try to restart. If F3 returns immediately or after a brief run, do not keep resetting repeatedly—this indicates a persistent fault.

3. Inspect the external flue terminal and air intake: from outside, check for obvious blockages (bird nests, leaves, mud, snow, debris) and remove any safe exterior obstructions. Do not insert objects into the flue.

4. Look for signs of water or leaks around the boiler and pipework—wet wiring, corrosion or stains inside the casing (if you can see them without removing the casing) can indicate internal water damage. If you find wet wiring or evidence of internal water, isolate power and call an engineer.

5. Listen for unusual noises: grinding, whining or bearing noises heard before the fault appeared are a sign of mechanical fan wear.

If the simple checks above do not clear the fault, call a Gas Safe registered engineer. When contacting them, report the F3 code, describe any audible symptoms, whether a reset was attempted, and whether you found external blockages or water.

What the engineer will check and typical diagnostic/fix steps (professional actions):

1. Confirm the fault with diagnostic tools and examine the fault log on the PCB to see when and how the F3 triggered.

2. Visually inspect and test the flue and air intake for blockages or damage and clear or replace flue components if required.

3. Check the fan motor and assembly: measure supply to the fan, test fan motor operation, check bearings for seizure or excessive play, and measure fan speed where applicable. Replace the fan assembly if motor or bearings are faulty.

4. Inspect wiring and connectors between the fan and PCB: reseat loose connectors, replace damaged wiring, and dry or replace any wiring affected by leaks. Corroded connectors should be renewed.

5. Check the PCB: if wiring and fan are OK but the PCB shows faults or erratic signals, the board may need repair or replacement. A wet or burnt PCB can mis-report errors and often requires replacement.

6. Trace and repair any internal water leaks if present (pump, heat exchanger, seals). Repairing the source of the leak is essential before replacing electrical components to prevent repeat faults.

7. After repairs, the engineer will run the boiler through start-up and safety checks, confirm correct fan speed and combustion/pressure where necessary, and clear the fault codes. They will confirm safe operation before leaving.

Final notes and advice:

1. Do not attempt to replace the fan, PCB or internal wiring yourself unless you are Gas Safe registered. Gas appliance repairs and gas-side work must only be carried out by a qualified engineer.

2. If the boiler remains locked out or you have recurring F3 faults after an engineer has fixed the issue, request a full diagnostic report and that the engineer checks for underlying causes such as intermittent water ingress or flue damage.

3. To help prevent future faults, arrange annual servicing by a Gas Safe engineer and keep the external flue/air intake clear of debris. Keep a record of fault occurrences and any audible warnings to help with diagnosis.