Error F3

Safety first:

1) If you smell gas or suspect carbon monoxide, do not stay inside. Turn off gas at the meter if you can do so safely, turn off the appliance if possible, ventilate the property, leave the building, and call the emergency gas number and a qualified engineer. Do not attempt internal repairs.

2) If you are not smelling anything dangerous, isolate electrical supply to the boiler only when instructed below for safe checks. Do not remove the boiler cover or perform any work that requires opening the appliance unless you are a qualified engineer.

Initial homeowner checks you can safely do:

1) Note the exact display and conditions (F3, any other letters, whether burner light is on/off). Try a simple restart first: press the boiler RESTART button as described in the manual, or switch the boiler to BOILER OFF, wait two minutes, then back to BOILER ON. If the fault clears and the boiler runs normally, monitor for reoccurrence and call an engineer if it returns.

2) Confirm mains power and external controls: check the boiler has power (fuse, RCD, switches), that the programmer/room thermostat is calling for heat if you expect heating/hot water, and that the mains supply appears stable.

3) Visually inspect the external flue terminal and air intake outside the building for obvious blockages (leaves, bird nest, debris) from ground level only. If you see a blockage and can remove it safely from the ground, do so. If it requires ladder/roof access or you are unsure, do not attempt — call an engineer.

4) Listen for abnormal noises when you attempt a restart (grinding, loud rumble or no sound when fan should run). Note any prior history of banging or unusual fan noise; that helps the engineer with diagnosis.

5) If there has been recent water ingress or leaks near the boiler, or the boiler has been moved/installed recently, note that down; wet wiring and disturbed connections are common causes.

What to avoid doing yourself:

- Do not remove the boiler casing, fan shroud, or perform internal electrical checks unless you are a qualified engineer. Fan replacement and wiring repairs are not DIY tasks on gas appliances.

- Do not attempt to bypass safety devices or run the boiler with the fault present.

Diagnostic steps for a qualified engineer (what you should tell them):

1) They will check for stored fault history on the PCB and verify fan speed feedback to the control board during ignition sequence.

2) They will inspect the flue and terminal for restriction or damage and verify correct fan operation and airflow against manufacturer settings.

3) They will check the fan motor, bearings and spinner for free rotation and noise, and measure supply to the fan motor and fan feedback sensor signals.

4) They will inspect wiring harnesses and connectors for corrosion, wetness, damage or loose connections and check related fuses and the PCB for faults.

5) If required they will replace the fan assembly or motor, repair wiring, or address PCB faults and then run the boiler through a full sequence and safety checks.

When to call a professional:

- If the F3 fault persists after a restart and external flue/vent checks, switch the boiler off and call a Gas Safe registered engineer (UK) or RGII (Ireland). Any internal work, fan replacement, wiring repair, or PCB assessment must be carried out by a registered engineer.

- Also call a professional immediately if you detect gas smell, suspect carbon monoxide, or if you are uncomfortable performing the safe external checks above.

What to tell the engineer when they arrive:

- The exact fault code (F3), what happened before it appeared, any noises you heard, whether you tried a restart and the result, whether the flue/inlet was blocked and whether there has been any water leak or recent works on the boiler. This information will speed diagnosis.

Summary:

Carry out only the safe exterior checks and a permitted restart. Do not open the boiler or attempt internal repairs. Because the fan is safety-critical, a persistent F3 should be fixed by a Gas Safe/RGII registered engineer who can correctly diagnose and replace fan components, repair wiring, or address PCB issues.