Andrews A06 Fault Code: Causes, Fixes & Repair Costs
What does the Andrews A06 fault code mean?
The A06 code signals that the boiler has detected an unsafe condition and locked itself out as a precaution. On most Andrews and Vokera-heritage boilers using the A0x fault format, A06 indicates a flue overheat — the temperature in the flue has exceeded its safe operating threshold, prompting an automatic shutdown. On certain Ferroli models that share this same fault-code numbering convention, A06 can alternatively indicate a no-flame condition, meaning the boiler attempted to ignite but could not confirm a stable burner flame. Because these two manufacturers share manufacturing roots and fault-code conventions, the correct meaning for your specific appliance should always be confirmed against your model's manual or by a Gas Safe registered engineer. Whichever definition applies, the boiler will not restart until the underlying issue is resolved.
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
- Blocked or obstructed flue Common
Bird nests, debris, soot build-up, or a dislodged terminal cap can all restrict the flow of exhaust gases through the flue. When gases cannot escape efficiently, heat backs up and the flue overheat sensor triggers a lockout. This is the most common cause of an A06 on flue-overheat variants.
- Faulty or failing fan Common
The fan is responsible for drawing combustion gases out through the flue. If it runs too slowly, intermittently, or not at all, exhaust gases remain in the heat exchanger and flue for too long, causing temperatures to rise. A worn motor, damaged impeller, or faulty wiring to the fan can all produce this fault.
- Incorrect or deteriorating flue installation Sometimes
A flue that was installed at the wrong angle, with too many bends, or that has partially separated at a joint will restrict gas flow even without a physical blockage. This can cause localised overheating and repeated A06 lockouts that worsen over time.
- Faulty flue overheat thermostat or sensor Sometimes
The thermal sensor that monitors flue temperature can develop an open circuit or give inaccurate readings as it ages. If it is triggering A06 prematurely when flue temperatures are actually within safe limits, the sensor itself may need replacing rather than the flue or fan.
- Ignition or flame-sensing failure (Ferroli no-flame variant) Sometimes
On models where A06 means no flame detected, the most likely culprits are a dirty or cracked spark electrode, worn ignition leads, a contaminated flame sensor (ionisation probe), or a fault in the ignition module. The boiler fires but cannot confirm combustion, so it locks out.
- PCB fault Rare
If the boiler's printed circuit board is misreading sensor signals or failing to correctly control the fan or ignition sequence, it can trigger A06 spuriously. This is relatively uncommon and is usually suspected only after other components have been checked and cleared.
How to fix it
- Check for an obvious flue obstruction from outside DIY safe
Go outside and look at the flue terminal on the wall or roof. Check whether anything visible — such as a bird nest, leaves, or debris — is blocking the outlet. Do not attempt to dismantle the flue yourself, but noting what you can see will be useful information for the engineer.
- Verify your gas supply is live DIY safe
Turn on another gas appliance such as a hob. If it lights normally, your gas supply is active and the issue is boiler-specific. If other appliances also fail, contact your gas supplier. If you smell gas at any point, leave the property immediately, do not operate any switches, and call the National Gas Emergency line on 0800 111 999.
- Reset the boiler once or twice DIY safe
Locate the reset button — usually a flame symbol on the boiler's control panel — and hold it for a few seconds until the boiler attempts to restart. Do this no more than two or three times. If the A06 code returns promptly each time, repeated resets will not resolve the underlying cause and may mask a developing safety issue.
- Have a Gas Safe engineer inspect and clear the flue Gas Safe engineer
A registered engineer will carry out a full flue inspection, checking for blockages, correct pitch, secure joints, and adequate terminal clearance. Where a blockage is found they will clear it safely; where the flue configuration is non-compliant they will advise on remedial work.
- Have the fan tested and replaced if necessary Gas Safe engineer
The engineer will check fan speed, current draw, and wiring integrity. A fan running outside its specified parameters will be replaced. This is one of the more common component-level fixes for an A06 flue overheat fault.
- Have the flue overheat sensor or thermostat checked Gas Safe engineer
If the flue and fan are both found to be in good condition, the engineer will test the thermal sensor that triggered the lockout. A sensor with an open circuit or drifted calibration will be replaced.
- Have ignition and flame-sensing components inspected (Ferroli no-flame variant) Gas Safe engineer
If your model uses A06 for a no-flame fault, the engineer will inspect the spark electrode for cracking or carbon deposits, test the ignition leads, and clean or replace the ionisation probe. If ignition components are serviceable but the fault persists, the ignition control module will be assessed.
- Call a Gas Safe registered engineer if the fault persists Gas Safe engineer
If the A06 code continues to appear after the steps above have been worked through, an engineer should carry out a full system diagnostic including PCB assessment. Do not continue to run the boiler in a fault condition — a flue overheat lockout exists to protect you and your property.
Parts you may need
- Flue fan / fan motor assembly · from £95
- Flue overheat thermostat / thermal fuse · from £25
- Spark ignition electrode · from £30
- Ionisation / flame sensing probe · from £28
- Ignition lead set · from £20
- Printed circuit board (PCB) · from £180
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 £120–£350, depending on the underlying cause.
Frequently asked questions
Is the Andrews A06 fault dangerous — can I keep using my boiler?
You should not attempt to keep the boiler running while it is showing an A06 lockout. If the code indicates flue overheat, it means the boiler has detected temperatures beyond its safe limit and has shut down to protect you. Running a boiler with a compromised flue risks carbon monoxide escaping into your home. Switch the boiler off and arrange for a Gas Safe engineer to inspect it promptly.
Why does my boiler show A06 only in cold weather?
Cold weather is a common trigger for flue-related faults because condensate pipes can freeze and block, and because thermal expansion and contraction can worsen partially dislodged flue joints. A fan motor that is borderline may also struggle in very cold conditions. If the A06 appears reliably in winter and clears in warmer months, mention this pattern to your engineer — it points strongly towards a flue or fan issue rather than an ignition fault.
How much does it typically cost to fix an A06 fault?
Most homeowners pay somewhere between £120 and £350 all-in, depending on what is found. A flue unblock or fan replacement tends to sit in the lower-to-middle part of that range, while a sensor replacement is usually at the lower end. PCB replacement is less common but significantly more expensive — typically £400 or more including parts and labour — and if your boiler is over ten years old, it may be worth comparing that cost against a new boiler installation.
My boiler manual says A06 means no flame, but this page mentions flue overheat — which is correct?
Both definitions exist within the A0x fault code family used by Andrews, Vokera, and Ferroli appliances, which share a common manufacturing heritage. Flue overheat is the most widely documented meaning for A06 on Vokera and Andrews units, while no-flame is documented on certain Ferroli variants. The definitive answer for your specific appliance is in its installation or user manual. If you no longer have the manual, a Gas Safe engineer can cross-reference your model number to confirm the correct interpretation before starting diagnostic work.