Buderus 3A 264 Fault Code: Causes, Fixes & Repair Costs
What does the Buderus 3A 264 fault code mean?
The 3A 264 fault code indicates that the boiler fan has stopped or failed during operation. On Buderus boilers, the broader 3A fault class relates to the differential pressure switch opening unexpectedly, but when the sub-code 264 accompanies it, the specific diagnosis is that the fan unit itself has ceased to operate. The fan is a critical safety component: it supplies combustion air to the burner and expels harmful exhaust gases — including carbon monoxide — through the flue. Before the boiler is allowed to fire, the PCB checks for a signal confirming the fan is spinning. If that signal is absent or lost mid-operation, the boiler locks out and displays 3A 264 to protect occupants from potentially dangerous flue gas spillage.
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
- Seized or burnt-out fan motor Common
After years of continuous use, the motor windings can burn out or the internal bearings can deteriorate to the point where the fan can no longer rotate. This is the single most common reason for a 3A 264 lockout and typically requires a full fan unit replacement.
- Fan blade blockage or physical damage Common
Debris drawn into the air intake — dust build-up, insulation fibres, or small foreign objects — can jam the fan blades. Damaged blades from age or impact also reduce rotational speed, which the PCB detects as a fan failure.
- Loose wiring or connector fault Common
Vibration over years of operation can work connectors loose between the fan and the PCB. If the speed-feedback signal from the fan is interrupted, the boiler locks out even if the fan motor itself is still functional. A thorough wiring inspection often resolves this without replacing the fan.
- Blocked or obstructed flue Sometimes
A flue blocked by a bird's nest, dead bird, leaves, or other debris creates excessive back-pressure. The boiler detects the pressure anomaly and shuts down. This can also trigger the wider 3A class fault before the 264 sub-code appears.
- Faulty air pressure switch Sometimes
The air pressure switch monitors whether the fan is creating sufficient airflow before allowing ignition. A diaphragm split, a blocked sensing tube, or a failed switch contact can prevent the boiler from receiving the all-clear signal, mimicking a fan fault even when the fan itself is healthy.
- PCB fault Rare
In rare cases the PCB sends incorrect commands to the fan or fails to recognise a valid fan-speed signal. This results in a lockout code even when all fan components are in good working order. PCB faults are typically diagnosed only after all other causes have been eliminated.
How to fix it
- Check for an obvious power or gas supply issue DIY safe
Confirm the gas supply is turned on at the meter and that other gas appliances in the property are working normally. Also check that the boiler has a stable electricity supply and hasn't tripped a circuit breaker. A momentary supply interruption can occasionally cause a spurious 3A 264 lockout.
- Attempt a single boiler reset DIY safe
Press and hold the boiler's reset button for approximately 2–3 seconds as described in your Buderus user guide. Stand back and observe whether the boiler starts up normally. Do not attempt more than two or three resets in total — repeated reset attempts when the fan has genuinely failed can stress the ignition components and will not resolve the underlying fault.
- Listen and look at the fan area (do not touch internal components) DIY safe
With the boiler casing in place, listen during a restart attempt for any sound of the fan spinning. A complete absence of noise, a grinding sound, or a short burst followed by lockout all indicate a mechanical fan problem. Note what you hear and report it to your engineer — this saves diagnostic time.
- Check the flue terminal outside DIY safe
Go outside and visually inspect the flue terminal on the wall or roof. Look for obvious blockages such as a bird's nest, leaves piled against the grille, or debris covering the outlet. Do not insert anything into the flue. If you can see a clear blockage and safely reach it, gently remove loose debris from the outside of the grille only.
- Engineer inspection of fan, wiring, and connectors Gas Safe engineer
A Gas Safe registered engineer will remove the boiler casing and carry out a systematic check of the fan motor, its electrical connectors, and the wiring loom back to the PCB. Loose or corroded connectors are re-seated or replaced. The fan blades are checked for dirt, damage, or obstruction.
- Engineer inspection of the air pressure switch and sensing hoses Gas Safe engineer
The engineer checks the pressure switch diaphragm, sensing tubes, and electrical contacts. Blocked or split sensing hoses are replaced. A faulty switch is swapped out for a genuine Buderus part to restore correct pressure monitoring.
- Engineer flue inspection and clearance Gas Safe engineer
If a flue blockage is suspected, the engineer carries out a full flue inspection, removes any obstruction, and — where no flue guard is fitted — recommends or installs one to prevent recurrence. Combustion readings are taken after clearance to confirm safe operation.
- Fan unit replacement if motor has failed Gas Safe engineer
Where the motor is confirmed burnt-out or seized, the engineer replaces the complete fan assembly with a genuine Buderus replacement unit. After fitting, combustion must be measured and adjusted if necessary — this is a legal requirement for gas work and cannot be skipped.
- PCB diagnosis and replacement if all else is ruled out Gas Safe engineer
If the fan, wiring, pressure switch, and flue all check out correctly, the engineer will test the PCB outputs. A confirmed PCB fault requires board replacement, which is typically one of the more expensive repairs on this range.
- Call a Gas Safe registered engineer Gas Safe engineer
If the boiler does not start normally after your single reset attempt, contact a Gas Safe registered engineer. Given that a failed fan can allow exhaust gases to accumulate inside the property, this fault should not be left unattended. Ensure you have a working carbon monoxide alarm in the property while waiting for the engineer.
Parts you may need
- Buderus replacement fan unit (GB142/GB072 compatible) · from £140
- Air pressure switch · from £45
- Fan wiring harness / connector set · from £25
- Flue terminal guard · from £15
- PCB (Printed Circuit Board) · from £280
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 £200–£400, depending on the underlying cause.
Frequently asked questions
Is it safe to keep using my Buderus boiler while fault code 3A 264 is showing?
No. When the fan stops, exhaust gases including carbon monoxide may not be safely expelled through the flue. The boiler locks itself out for exactly this reason. Do not attempt to override the lockout or repeatedly reset the boiler. Make sure you have a working carbon monoxide detector in the property and arrange for a Gas Safe registered engineer to inspect the boiler promptly.
Can I fix the Buderus 3A 264 fault myself?
The only actions a homeowner should take are checking the gas and power supply are on and attempting a single reset. All internal work — inspecting the fan, testing the wiring, replacing components, or clearing an internal flue blockage — must be carried out by a Gas Safe registered engineer. Working on gas appliances without registration is illegal in the UK and extremely dangerous.
How much does it cost to repair a Buderus 3A 264 fault in the UK?
Most people pay between £200 and £400 all-in for parts and labour, with a fan unit replacement being the most common repair. The fan component itself typically costs £100–£200, with labour adding roughly £100–£150 on top. If the fault turns out to be a simpler wiring or pressure switch issue, the bill is usually at the lower end of that range. A PCB replacement is considerably more expensive — often £350–£600 including labour — but that outcome is comparatively rare and would only be recommended after all other causes are ruled out.
Why does the 3A 264 code sometimes appear with just '3A' on the display?
The 3A fault class covers differential pressure switch issues more broadly, while the 264 sub-code narrows the diagnosis to the fan having stopped. Some older Buderus displays or control units may only show the class code 3A without the numeric sub-code. If you see just 3A, an engineer will still check the fan, its wiring, the pressure switch, and the flue — the same diagnostic pathway applies whether or not 264 is visible alongside it.
My Buderus boiler is quite old — is it worth replacing the fan or should I get a new boiler?
If your boiler is within its expected service life (typically up to around 15 years with good servicing) and is otherwise in good condition, a fan replacement at £200–£400 is usually worthwhile. For boilers that are older, out of manufacturer warranty, and showing other signs of wear, it may be more cost-effective to put that money towards a new, more efficient condensing boiler. Ask your Gas Safe engineer for an honest assessment before committing to the repair.