Andrews A09 Fault Code: Causes, Fixes & Repair Costs
What does the Andrews A09 fault code mean?
On Andrews water heaters and boilers, the letter 'A' in a fault code indicates a full lockout — the appliance has shut down completely and will not restart without a manual reset. A09 specifically points to a safety-critical issue with flame detection or gas valve integrity. In practical terms, this means the control system has detected a flame signal when no flame should be present (a 'false flame' condition), or has identified a problem with the gas valve failing to close fully, or — on certain models — a fault with the flue thermistor circuit. All three scenarios trigger an immediate lockout because they represent a potential safety hazard. Because Andrews appliances span several product families (MAXXflo, ECOflo, HIflo, COMBIflo and others), the precise meaning of A09 can vary slightly between control board variants, so always cross-reference with your model's data plate and service documentation.
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 leaking gas valve Common
If the gas solenoid valve does not close completely when the burner shuts off, a trickle of gas can continue to burn. The ionisation circuit picks up this residual flame and triggers an A09 lockout. Internal valve wear, debris on the valve seat, or a failed solenoid coil are the usual culprits.
- Contaminated or failed flame detection electrode Common
The ionisation probe measures electrical conductivity through the flame to confirm burner status. Carbon deposits, cracking, or a short to earth can cause it to report a flame signal even when the burner is completely off, mimicking the false-flame condition that drives A09.
- Flue thermistor fault (model-dependent) Sometimes
On Andrews appliances using certain control board configurations, A09 is linked to the flue thermistor or its associated counter circuit. A failed sensor, damaged sensor wiring, or a poor connection at the board can cause the control system to register an out-of-range or contradictory reading and lock out.
- Wiring fault between gas valve, electrode, or PCB Sometimes
Loose terminals, chafed cable insulation, or corrosion on connectors in the flame detection or gas valve circuit can generate spurious signals that the control board interprets as a false flame. This is particularly common on older or heavily used commercial units where cables are routed near hot surfaces.
- Faulty PCB or flame monitor circuit Rare
Moisture ingress, component ageing, or physical damage to the printed circuit board — specifically the flame monitor section — can cause incorrect flame signal processing. If all other components test correctly, the PCB itself may be generating the false-flame reading internally.
How to fix it
- Attempt a single manual reset DIY safe
Locate the reset button on the Andrews appliance control panel. Press and hold it for approximately 3–5 seconds — a brief tap is often insufficient to register. Allow the unit to complete its start-up sequence. If it locks out again immediately or within a short time, do not reset a second time without first checking the steps below.
- Limit resets to no more than two attempts DIY safe
If the boiler locks out again after your first reset, you may try once more. Beyond two failed resets, stop. On an A09 fault — which can involve the gas valve not closing properly — repeated resets could introduce unburnt gas into the flue or combustion chamber, creating a genuine safety risk. Note how quickly the lockout returns, as this information will help the engineer diagnose the fault.
- Check for a gas supply issue DIY safe
Confirm that the gas supply to the property is on and that other gas appliances (hob, separate boiler) are working normally. If there is no gas supply across the property, contact your gas supplier rather than an engineer. Do not attempt to operate any gas isolation valves on the Andrews unit itself.
- Note the fault code display and model details DIY safe
Record exactly what appears on the control panel display — the code, any sub-code, and how quickly the lockout occurs after a reset attempt. Find the data plate on the unit and note the model name, model number, and serial number. This information allows the engineer to pull the correct wiring diagram and confirm which variant of A09 applies to your specific control board.
- Do not attempt to inspect or touch gas or electrical components Gas Safe engineer
The gas valve, ionisation electrode, flue thermistor, PCB, and all associated wiring must only be inspected, tested, or replaced by a Gas Safe registered engineer. Andrews appliances are commercial-grade units; unauthorised intervention can void any remaining warranty and creates a serious safety and legal risk.
- Contact a Gas Safe registered engineer with commercial heating experience Gas Safe engineer
Call Andrews Water Heaters' technical support line or arrange a visit from a Gas Safe registered engineer familiar with Andrews or Baxi Commercial products. The engineer will test the gas valve for internal leakage and correct closure, inspect and clean or replace the ionisation electrode, check the flue thermistor and wiring where applicable, examine all wiring harness connections throughout the flame detection circuit, and replace any failed components such as the gas valve, thermistor, or PCB.
Parts you may need
- Gas valve (solenoid assembly) · from £180
- Ionisation / flame detection electrode · from £35
- Flue thermistor / exhaust temperature sensor · from £45
- Printed circuit board (PCB) · from £320
- Electrode lead / high-tension cable · from £25
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 £180–£500, depending on the underlying cause.
Frequently asked questions
Is it safe to keep resetting my Andrews boiler on an A09 fault?
No — limit yourself to two reset attempts. A09 can indicate that the gas valve is not closing fully, meaning unburnt gas could accumulate if you keep forcing restarts. If the boiler locks out again after two tries, leave it off and call a Gas Safe registered engineer. If you smell gas at any point, turn off the gas at the meter, open windows, avoid electrical switches, and call the National Gas Emergency Service on 0800 111 999.
How much does it cost to fix an Andrews A09 fault?
Most repairs that trigger an A09 lockout fall in the range of £180–£500 including parts and labour. Replacing the ionisation electrode or flue thermistor sits at the lower end of that range, while a full gas valve replacement typically costs £250–£400 all-in. A PCB replacement can push beyond £500 once parts and labour are combined, but this is less commonly the root cause. Always get at least three quotes from Gas Safe registered engineers and confirm they have experience with commercial Andrews or Baxi appliances.
Which Andrews models can show an A09 fault code?
The 'A' prefix lockout convention is used across Andrews' main water heater and boiler ranges, including the MAXXflo, ECOflo, HIflo, and COMBIflo product families. However, the precise meaning of A09 depends on the control board variant fitted to your specific unit, so it is worth checking your model's installation and servicing manual or contacting Andrews technical support with your model and serial number.
Can I fix an A09 fault myself?
Only the most basic checks are safe for a homeowner: confirming the gas supply is on, attempting up to two resets, and noting the fault code and model details. Everything else — testing the gas valve, replacing the ionisation electrode, checking the PCB or flue thermistor — must be carried out by a Gas Safe registered engineer. Andrews appliances are commercial units and are covered by strict legal requirements around who may service gas fittings. Attempting DIY repairs on gas components is illegal for uncertified individuals and could invalidate your warranty.