Error 84

Safety first

1) If you smell gas or suspect a carbon monoxide leak: evacuate everyone immediately, call the emergency gas service and your local emergency services. Do not attempt repairs. 2) If you are not electrically competent or not Gas Safe registered, stop at the visual checks below and call a qualified engineer for anything beyond that.

Initial homeowner checks (safe, non-invasive)

1) Note the exact code, any preceding events, and take a photo of the display. 2) Reset the boiler once: press and hold the reset button for 5–10 seconds (follow the boiler’s reset instructions). Wait to see if the boiler starts normally. Do not repeatedly reset if it returns straight away. 3) Check mains power and fused spur to the boiler and ensure the timer/room thermostat is asking for heat (no supply or no call for heat can complicate diagnostics). 4) Check the external flue terminal for obvious blockages (bird nest, debris, leaves). Only clear from ground level and only if it is safe to do so; do not climb without proper precautions. 5) Check for visible water ingress or corrosion around the flue/air intake which could impair the fan.

Further diagnostic steps (only if you are competent and have isolated power)

1) Isolate electrical supply at the fused spur before opening the boiler casing. Never work live unless you are a qualified electrician/engineer. 2) Remove the casing and visually inspect the fan, wiring and connector for damaged, burnt or corroded pins and for signs of water or debris in the fan housing. 3) Manually spin the fan impeller by hand (after electrical isolation). If it does not spin freely or feels rough/gritty, the fan motor or bearings are likely failed and the fan will need replacement. 4) If you are qualified to use a multimeter and safely work live: with a colleague calling for heat (engineer action), measure whether the PCB is supplying the correct mains voltage to the fan when the boiler attempts to start. If voltage is present but the fan does not run, the motor is faulty. If no voltage is present, the fault may be the PCB, wiring, or sensors. 5) Check continuity of the fan motor windings (isolated) if you know how to interpret the readings; an open winding indicates a failed motor. 6) Inspect the fan rotor/impeller for foreign objects, heavy soot or damage; remove debris only when isolated and safe to do so.

What to do next and when to call a professional

1) If a temporary reset cleared the fault and the boiler runs normally for a sustained period, monitor pressure and operation. If the fault returns, call a Gas Safe registered engineer. 2) If you find the fan seized, damaged, or the fan motor fails electrical tests, the fan will need replacing — this must be done by a qualified engineer. 3) If wiring, connector damage, or PCB non-supply to the fan is suspected, do not attempt PCB repairs yourself; call a qualified engineer. 4) Do not continue to use the boiler if the fan fault persists — leave the appliance off and use alternative heating if needed.

Notes and good practice

1) Repeated resets can mask an underlying fault and may cause more damage; avoid repeated attempts. 2) Take photos and note the fault code and any findings (helpful to the attending engineer). 3) Provide the engineer with the full boiler model and any error history. 4) Always use a Gas Safe registered heating engineer for repairs to combustion components, fan replacement, PCB work or gas-related work. No plumbing or electrical cost estimates are given here; the engineer will advise on parts and labour when diagnosed.