Andrews A05 Fault Code: Causes, Fixes & Repair Costs
What does the Andrews A05 fault code mean?
The A05 code indicates that the boiler or water heater has shut itself down because it cannot confirm the combustion fan is running correctly. The fan is responsible for expelling harmful flue gases safely out of the appliance — without a confirmed fan signal, the unit will refuse to fire as a safety precaution. This lockout protects against dangerous gases building up inside the property. The fault may point to a failed fan motor, a wiring issue between the fan and the control board, a blocked flue or condensate pipe, a faulty air pressure switch, or in some cases a PCB fault mimicking fan failure.
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
- Faulty or worn fan motor Common
Over time the fan motor bearings can deteriorate and the motor windings can burn out, causing the fan to spin too slowly or stop altogether. The PCB cannot confirm a safe fan speed, so it triggers the A05 lockout. This is the single most common root cause engineers find on this code.
- Wiring harness fault between fan and PCB Common
The fan communicates its speed and status to the PCB through a wiring harness. Loose connectors, chafed cables, or corroded terminals can break that signal even if the fan motor itself is healthy. Engineers typically inspect the wiring harness first before condemning the fan.
- Blocked flue or condensate pipe Sometimes
A blocked flue — caused by debris, a bird's nest, ice, or a damaged terminal — prevents the fan from moving air at the correct pressure. Similarly, a frozen or blocked condensate pipe (especially common in cold snaps) can trigger safety shutdowns that manifest as fan-related codes. The air pressure switch detects the abnormal pressure and feeds a fault signal back to the PCB.
- Faulty air pressure switch Sometimes
The air pressure switch monitors whether flue gases are being vented safely. If the switch diaphragm splits, the switch sticks, or its sensing tube becomes blocked, it can incorrectly report that the fan is not working even when it is operating normally. A Gas Safe engineer can test the switch with a multimeter.
- PCB fault Rare
The PCB controls power to the fan and reads its feedback signal. A failing PCB may cut power to the fan, misread the speed signal, or lock out falsely. PCB faults typically appear alongside other unexplained electrical symptoms and are diagnosed only after the fan, wiring, and pressure switch have been ruled out.
How to fix it
- Check your gas supply is live DIY safe
Make sure other gas appliances in the property (hob, gas fire) are working normally. If there is no gas supply to the house, contact your gas supplier before doing anything else. A loss of gas pressure can sometimes prevent the fan sequence from completing.
- Look and listen when the unit tries to start DIY safe
Stand near the appliance and attempt a restart. You should hear the fan spin up — a low hum or whirr — before ignition is attempted. If you hear nothing, or the fan sounds laboured or intermittent, that points strongly to a fan or wiring problem. Note what you observe to report to the engineer.
- Inspect the flue terminal for obvious blockages DIY safe
Go outside and look at where the flue exits the building. Check for visible obstructions such as leaves, a bird's nest, ice, or a damaged terminal cap. Do not attempt to dismantle any flue pipework — simply note and photograph any obstruction. A clear external terminal is a good sign; if blocked, call an engineer to clear it safely.
- Thaw a frozen condensate pipe if cold weather is a factor DIY safe
In freezing temperatures the condensate pipe — usually a white plastic pipe running from the boiler to an external drain — can ice up and cause safety shutdowns. You can carefully pour warm (not boiling) water over the visible external section or wrap it with a warm damp cloth to thaw it. Once thawed, reset the boiler. Insulating the pipe with foam lagging helps prevent a recurrence.
- Reset the boiler (up to two or three times) DIY safe
Press and hold the reset button as described in your Andrews appliance manual. Wait for the startup sequence to complete. If the A05 code clears and the unit runs normally, monitor it over the next hour. If the fault returns or does not clear after two or three reset attempts, stop resetting — repeated failed ignitions can cause other issues — and move on to calling an engineer.
- Call a Gas Safe registered engineer to diagnose and repair the fault Gas Safe engineer
If the fault persists after the checks above, the repair requires a qualified professional. The engineer will test the fan motor speed and operation, check the wiring harness for continuity and connection quality, test the air pressure switch with a multimeter, inspect the flue and condensate system internally, and test the PCB fan-signal outputs. Do not attempt to open the casing, touch internal wiring, or handle any components yourself.
Parts you may need
- Combustion fan / flue fan motor · from £130
- Air pressure switch · from £45
- Fan wiring harness · from £30
- PCB (control 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 £150–£375, depending on the underlying cause.
Frequently asked questions
Is the Andrews A05 code dangerous — should I keep using the appliance?
The boiler or water heater will have locked itself out, so it will not fire while the fault is active. That means there is no immediate risk of carbon monoxide from combustion, but you also have no hot water or heating. Do not attempt to bypass the lockout or force the unit to run — the fan lockout exists precisely to prevent unsafe venting of flue gases. Get the fault diagnosed promptly.
Can I fix the Andrews A05 fault myself?
A few homeowner-safe checks are worthwhile: confirming the gas supply is on, listening for fan noise on startup, inspecting the external flue terminal for blockages, thawing a frozen condensate pipe in cold weather, and attempting a reset up to two or three times. Beyond that, opening the casing or touching internal components requires a Gas Safe registered engineer. Fan motors, wiring harnesses, air pressure switches, and PCBs must all be worked on by a qualified professional.
How much does it cost to fix an A05 fan fault on an Andrews appliance?
For the most common repair — replacing the fan motor — expect to pay roughly £150 to £375 including parts and labour, depending on the specific Andrews model and your location. An air pressure switch swap typically costs £100 to £180 all in. If the PCB turns out to be the culprit, parts alone can run to £250 to £400 or more, making it a significantly pricier repair — worth mentioning to your engineer before authorising the work so you can weigh it against the age of the appliance.
Why does the A05 code keep coming back after I reset it?
A fault that clears on reset but returns within hours or days usually means an underlying component is failing intermittently — most often a fan motor with worn bearings, a loose wiring connector that vibrates back into contact, or an air pressure switch that is borderline functional. Each reset without a proper repair simply delays the inevitable and can mask a worsening fault. Book a Gas Safe engineer to carry out a proper diagnostic rather than continuing to reset.