Andrews A16 Fault Code: Causes, Fixes & Repair Costs
What does the Andrews A16 fault code mean?
The A16 fault code indicates a gas valve failure on Andrews boilers built on the Ferroli platform. The boiler's control system has detected that the gas valve is not operating correctly — it may not be opening, closing, or responding to electrical signals as expected. Because the gas valve is a critical safety component controlling fuel delivery to the burner, the boiler will lock itself out and refuse to fire until the fault is resolved and a manual reset is performed. Note: A16 is documented across the Ferroli boiler range. Andrews Water Heaters (particularly gas-fired combi and system boilers) shares technical platforms with Ferroli under the BDR Thermea group, so if your boiler displays A16, the information on this page applies. Always cross-reference your specific model's manual if unsure.
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 gas valve Common
Over time the gas valve can deteriorate, with internal components becoming worn or seized. When the valve can no longer open or close reliably in response to the PCB's signals, the boiler detects the anomaly and triggers A16. This is the most frequent root cause seen by engineers attending this fault.
- Wiring fault between PCB and gas valve Common
The wiring loom connecting the printed circuit board to the gas valve can suffer from loose connections, corroded terminals, or damaged insulation — especially in older appliances or those in damp boiler cupboards. A break or short in this circuit mimics the same electrical signature as a failed valve and will trigger A16.
- Low or unstable mains voltage Sometimes
The gas valve's solenoid coils require sufficient mains voltage to actuate properly. If the supply voltage at the boiler drops below normal operating levels — due to a broader electrical issue in the property or a failing component on the PCB — the valve may fail to respond, triggering the lockout code.
- Failed PCB Rare
If the control board itself is unable to send the correct signal to the gas valve, the valve will not respond even though it is physically intact. A PCB fault can produce A16 as a secondary symptom. Engineers will typically rule out the valve and wiring first before suspecting the board.
How to fix it
- Check your gas supply is working DIY safe
Confirm that other gas appliances in your home — a gas hob, a gas fire — are functioning normally. If nothing gas-powered is working, contact your gas supplier rather than the boiler. If other appliances are fine, the gas supply to the boiler is likely adequate.
- Reset the boiler once or twice DIY safe
Locate the reset button on your boiler (usually a flame or restart symbol) and hold it for the duration specified in your manual, typically 3–5 seconds. Wait for the boiler to attempt ignition. If A16 clears and the boiler runs, monitor it closely. If the fault returns, do not keep resetting — repeated lockouts signal a genuine component fault that needs professional attention.
- Check for obvious electrical issues DIY safe
Look at the boiler display for any signs of power fluctuation, such as flickering or a dim screen. Check that the boiler's fused spur is switched on and that no fuses have tripped in your consumer unit. Do not open the boiler casing or touch any internal wiring.
- Call a Gas Safe registered engineer to inspect the gas valve and wiring Gas Safe engineer
An engineer will open the boiler casing and carry out electrical tests on the wiring loom between the PCB and the gas valve, checking for short circuits, open circuits, and loose connections. They will also test the valve's solenoid coils with a multimeter to determine whether the valve itself has failed.
- Gas valve replacement (engineer only) Gas Safe engineer
If testing confirms the valve is defective, the engineer will source and fit a compatible replacement gas valve. This involves isolating the gas supply, disconnecting the valve safely, fitting the new component, and carrying out a full gas-tightness test and functional check before signing off the repair.
- PCB inspection and replacement if required (engineer only) Gas Safe engineer
Should the valve and wiring both test as serviceable, the engineer will investigate the PCB as the source of the incorrect signal. PCB replacement is a specialist task involving careful component handling and a full system recommission afterwards.
Parts you may need
- Gas valve (Ferroli-platform compatible) · from £95
- Wiring loom / harness · from £35
- PCB (printed circuit board) · from £120
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–£320, depending on the underlying cause.
Frequently asked questions
Is the A16 fault code dangerous — should I stop using my boiler immediately?
The boiler will already have locked itself out when A16 appears, so it will not be firing or producing heat. You do not need to take any additional action to make the boiler safe, but you should not attempt to bypass the lockout or repeatedly reset it. Leave the boiler in its locked-out state and arrange for a Gas Safe engineer to attend. The fault involves the gas valve, which is a safety-critical component.
Can I fix an A16 fault myself?
No. Beyond checking your gas supply is on, attempting one or two resets, and checking your mains electrics, there is nothing safe a homeowner can do to resolve this fault. The gas valve and its wiring are inside the boiler casing, and working on gas-carrying components is illegal without Gas Safe registration. A qualified engineer is required.
How much does it cost to fix an A16 fault code in the UK?
For the most common repair — gas valve replacement including parts and labour — most homeowners pay in the region of £150 to £320. The valve component itself typically costs £80–£120 for a Ferroli-platform part, with the remainder covering engineer time. If the PCB is also at fault, costs can rise to £400–£500 or more. For an older boiler where multiple components are failing, it is worth getting a replacement quote alongside the repair quote.
My boiler says A16 but clears after a reset — do I still need an engineer?
Yes. A fault code that clears temporarily but keeps returning is a sign that a component is on the way out. Intermittent gas valve faults can become permanent without warning, leaving you without heating or hot water. It is also worth noting that repeatedly resetting a boiler with an active gas valve fault is not advisable on safety grounds. Book an engineer while the boiler is still working rather than waiting for a full breakdown.
Is Andrews A16 the same as Ferroli A16?
Effectively, yes. Andrews gas-fired combi and system boilers are built on the Ferroli technical platform — both brands sit within the BDR Thermea group and share components and control systems. The A16 fault code is well documented on Ferroli appliances and carries the same meaning (gas valve fault) on Andrews-badged versions of the same platform. If your boiler is a commercial Andrews water heater rather than a domestic gas boiler, the code numbering may differ, so check your specific model's documentation.