Alpha 0A5 Fault Code: Causes, Fixes & Repair Costs
What does the Alpha 0A5 fault code mean?
The 0A5 fault code on Alpha boilers indicates a fan-related fault. The boiler's control board has detected a problem with the flue fan — either it isn't running at all, isn't reaching the correct speed, or is returning unexpected feedback signals. Because the fan is responsible for pushing harmful combustion gases safely out through the flue, the boiler will lock out and refuse to fire until the fault is resolved. This is a safety-critical lockout that always requires attention.
General guidance only — not a substitute for professional advice, and not certified by a Gas Safe engineer. Always have your specific appliance assessed by a qualified professional. Any gas work must be carried out by a Gas Safe registered engineer. If you smell gas or suspect carbon monoxide, leave the property and call the National Gas Emergency line on 0800 111 999.
Common causes
- Worn or burnt-out fan motor Common
Over time, the motor windings inside the fan can burn out, or the bearings can degrade and seize. This is the single most common root cause of the 0A5 code. A failing motor may produce no sound at all on start-up, or may make a grinding or rattling noise before stopping.
- Loose or damaged electrical connections Common
The wiring harness connecting the fan to the PCB can work loose due to vibration, or individual wires can become corroded or chafed. A poor connection can cause the fan to cut out intermittently or fail to start, triggering the lockout even if the motor itself is still serviceable.
- Blocked or restricted flue or air intake Sometimes
A bird's nest, debris, or a kinked flue terminal can restrict airflow sufficiently for the control board to detect abnormal fan behaviour. The fan may be physically intact but unable to reach the correct speed against the additional resistance.
- PCB (printed circuit board) fault Rare
The PCB controls the fan speed and monitors its feedback signal. If the board develops a fault — such as a failed triac or a damaged fan-control circuit — it can either fail to send power to the fan or misread the tachometer signal, generating a 0A5 code even when the fan motor is undamaged.
How to fix it
- Check that the boiler's gas supply is on DIY safe
Make sure the gas isolation valve on the supply pipe to the boiler is open (handle in line with the pipe). Check that other gas appliances in the home are working normally to rule out a wider supply interruption.
- Inspect the external flue terminal for obvious blockages DIY safe
Go outside and visually inspect the flue outlet (usually on an external wall or roof). Look for a bird's nest, leaves, or other debris partially blocking the terminal grille. Do not attempt to dismantle any flue components — if you can see a clear obstruction, report it to your engineer.
- Attempt a single boiler reset DIY safe
Press and hold the reset button (or follow the reset procedure in your Alpha boiler's user guide) for the model you own. Allow the boiler to complete its start-up sequence. If the 0A5 code returns within a minute or two, do not keep resetting — repeated resets without fixing the underlying fault can mask worsening problems.
- Engineer: listen to fan behaviour on start-up Gas Safe engineer
A Gas Safe engineer will power the boiler and listen carefully during the fan pre-purge phase. Complete silence suggests no electrical supply is reaching the motor; unusual grinding, rattling, or squealing indicates mechanical bearing failure. This informs whether the fault is electrical or mechanical.
- Engineer: test fan wiring and connections Gas Safe engineer
The engineer will use a multimeter to check voltage at the fan terminals and continuity through the harness. Loose plug-in connectors will be reseated; corroded or damaged wires will be repaired or replaced. In many cases this alone resolves the fault.
- Engineer: replace the fan if faulty Gas Safe engineer
If electrical supply is confirmed good but the fan motor is unresponsive or noisy, the engineer will fit a replacement fan assembly compatible with the specific Alpha model. This is the most common billable repair for this fault code.
- Engineer: inspect and test the PCB if fan replacement does not resolve the fault Gas Safe engineer
If a new fan and confirmed good wiring still result in the 0A5 code, the PCB's fan-control circuitry is the likely culprit. The engineer may be able to repair the board or will advise on a PCB replacement. On older out-of-warranty boilers, the engineer may recommend comparing the repair cost against a new boiler installation.
- Call a Gas Safe registered engineer if the fault persists or you cannot resolve it yourself Gas Safe engineer
Fan faults on Alpha boilers are not a DIY repair. If you have not already done so, contact a Gas Safe registered engineer to diagnose and fix the 0A5 code safely. If your boiler is still within its Alpha warranty period, contact Alpha Heating Innovation directly — a valid annual service record is typically required to maintain warranty cover.
Parts you may need
- Alpha boiler fan assembly (model-specific) · from £130
- Fan wiring harness / plug connector · from £25
- PCB (printed circuit board) · from £220
The exact spare depends on your boiler's GC number (on the data badge). Check this against the part before buying.
Typical repair cost
Expect to pay roughly £225–£375, depending on the underlying cause.
Frequently asked questions
Is the Alpha 0A5 fault dangerous?
The 0A5 code means the boiler has locked itself out as a precaution — it will not fire while the fan fault is present. This is a safety feature. You should not attempt to bypass the lockout. The boiler is not actively dangerous in its locked-out state, but you should get it repaired promptly so combustion gases cannot build up if the boiler were somehow to operate without a functioning fan.
How much does it cost to fix an Alpha 0A5 fan fault in the UK?
For most homeowners the all-in cost (parts and labour) falls between £225 and £375. The fan assembly itself typically costs £100–£200 depending on the Alpha model, with the remainder being the engineer's labour. If the PCB also needs replacing, costs can climb towards £500 or more — which is when it's worth comparing the repair bill against the cost of a new boiler, particularly if your Alpha is more than eight to ten years old.
Can I reset my Alpha boiler to clear the 0A5 code?
You can try a single reset — occasionally a temporary signal glitch causes the lockout and a reset clears it permanently. However, if the 0A5 code returns straight away or after only a short run, the underlying fault has not gone away. Repeatedly resetting without fixing the root cause is not recommended and will not resolve a genuinely faulty fan motor or damaged wiring.
My Alpha boiler is still under warranty — who should I call for a 0A5 fault?
Contact Alpha Heating Innovation directly rather than booking an independent engineer. Alpha can arrange a warranty repair at no parts cost, provided you have kept up with annual services by a Gas Safe registered engineer as required by the warranty terms. Booking an independent engineer first without Alpha's authorisation may affect your warranty claim.