Andrews A01 Fault Code: Causes, Fixes & Repair Costs
What does the Andrews A01 fault code mean?
The A01 fault code on an Andrews boiler indicates that the control system attempted to start the burner but failed to detect a stable flame. Once the boiler tries to ignite and doesn't register a flame within the allotted time, it performs an automatic safety lockout to prevent unburnt gas from accumulating. This is a protective response, not a fault in itself — something upstream in the ignition sequence has gone wrong, and the boiler is refusing to run until the cause is resolved. Andrews Water Heaters are predominantly commercial and industrial units (found in hotels, leisure centres, and hospitals), so A01 faults on these systems should be treated with the same urgency as on any domestic boiler, though the scale of the equipment may mean diagnosis takes longer. Note that Andrews fault codes are model-specific; always cross-reference your unit's engineer manual or contact Andrews technical support if in doubt.
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
- Interrupted or absent gas supply Common
If the gas supply to the boiler is off, at low pressure, or intermittent, the burner simply cannot ignite. Check whether other gas appliances in the building — such as a hob or gas fire — are working normally. On properties with prepayment meters, a depleted credit balance is a surprisingly frequent cause of A01 lockouts, particularly overnight. Also confirm the isolation valve on the gas supply pipe to the boiler is fully open (handle in line with the pipe).
- Faulty or degraded ignition electrode Common
The ignition electrode produces the spark that lights the gas. Over time, electrodes accumulate carbon deposits, crack, or shift out of alignment, all of which can prevent a reliable spark. Damaged or corroded electrode leads produce the same result. This is one of the most frequent engineer findings on an A01 call-out, and the electrode is a relatively straightforward and affordable component to replace.
- Faulty or dirty flame sensor (ionisation probe) Common
Once ignition occurs, the flame sensor confirms to the PCB that a stable flame is present. If the sensor is coated with residue or has failed electrically, it won't send the correct confirmation signal — even if the burner is actually lit. The PCB then assumes no flame exists and locks the boiler out. A Gas Safe engineer can test the sensor's ionisation current and clean or replace it as needed.
- Gas valve not opening correctly Sometimes
The gas valve controls the flow of fuel to the burner. If it sticks shut or fails to open fully during an ignition attempt, insufficient gas reaches the burner and no flame is established. Gas valve issues can also be caused by a faulty solenoid or wiring problem. Because this involves direct gas system components, diagnosis and replacement must be carried out by a Gas Safe registered engineer.
- Blocked flue or malfunctioning fan Sometimes
The flue fan must establish the correct draught before the ignition sequence can proceed. If the fan is failing, running slowly, or the flue is partially blocked by a bird's nest or debris, the air pressure switch will not confirm adequate airflow. Without that confirmation, the PCB will not allow ignition to begin, which can present as an A01 lockout. Flue and fan issues are more common on older commercial Andrews units.
- PCB (printed circuit board) fault Rare
The PCB orchestrates the entire ignition sequence — signalling the fan, reading the pressure switch, opening the gas valve, and triggering the electrode. A fault on the PCB can cause it to send incorrect or mistimed signals, leading to an apparent ignition failure even when all other components are healthy. PCB diagnosis requires specialist test equipment and is always an engineer job. On older Andrews commercial units, PCBs can be expensive and sometimes difficult to source.
How to fix it
- Check the gas supply to the property DIY safe
Try a gas hob, gas fire, or another gas appliance. If none of them work, there is likely a supply issue — check your meter, confirm your credit if you have a prepayment meter, and contact your gas supplier if necessary. If other appliances work normally, the gas supply to the site is fine and the fault is within the boiler itself.
- Confirm the boiler's gas isolation valve is fully open DIY safe
Locate the isolation valve on the gas pipe leading directly to the boiler. The handle should be parallel to the pipe to indicate it is open. If it is perpendicular, it is closed — turn it so it aligns with the pipe. Do not touch any other valves or pipework.
- Reset the boiler once DIY safe
Press and hold the reset button (refer to your Andrews boiler's manual for its location — it varies by model). Wait at least two minutes before attempting the reset. If the boiler fires up and runs normally, monitor it over the next hour. If the A01 code returns immediately or after a short time, do not reset again — repeated resets will not fix an underlying fault and can mask the problem for an engineer.
- Call a Gas Safe registered engineer to diagnose and repair the fault Gas Safe engineer
If the boiler locks out again after a single reset, the cause is internal and must be investigated by a qualified professional. A Gas Safe engineer will test the ignition electrode and its leads, check the flame sensor's ionisation signal, verify gas valve operation and solenoid function, inspect the fan and flue draught, and test the PCB's ignition sequencing. Andrews commercial units may require an engineer with experience of commercial water heating systems — check that your chosen engineer is familiar with the Andrews range or contact Andrews technical support on 0330 123 3139 for a recommended engineer.
Parts you may need
- Ignition electrode and lead set · from £35
- Flame sensor / ionisation probe · from £20
- Gas valve · from £120
- Flue fan / combustion fan · from £180
- PCB (printed circuit board) · from £320
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–£380, depending on the underlying cause.
Frequently asked questions
Can I keep resetting my Andrews boiler to clear the A01 code?
You can attempt a single reset after checking the gas supply and waiting a couple of minutes — that is a legitimate first step. However, repeatedly resetting a boiler with an A01 fault is not a fix. If the lockout returns, the boiler is telling you something is wrong with the ignition system, and each failed ignition attempt causes unnecessary wear. Arrange an engineer visit rather than cycling through resets.
Is the A01 fault dangerous?
The boiler's lockout is actually the safety system working correctly — it has detected that ignition did not complete and has shut down to prevent unburnt gas from building up. Once locked out, the boiler is not actively releasing gas. You should not attempt to bypass the lockout or interfere with gas components. If you smell gas at any point, do not attempt a reset: leave the property, avoid using electrical switches, and call the National Gas Emergency Service on 0800 111 999 immediately.
How much does it cost to fix an A01 fault on an Andrews boiler?
Most A01 repairs fall in the £120–£380 range including parts and labour. A straightforward ignition electrode replacement typically costs £100–£200, while a flame sensor job is usually at the lower end of that range. Gas valve replacement tends to run £200–£350. PCB replacement is the most expensive common repair at £400–£600 or more including labour, and on an older Andrews commercial unit that cost should be weighed carefully against the age of the equipment and the price of a replacement unit.
Why does my Andrews boiler keep getting A01 faults repeatedly over months?
Recurring A01 faults usually point to a component that is degrading gradually rather than one that has failed outright — a worn ignition electrode slowly losing its ability to spark reliably, or a flame sensor that works intermittently. It can also indicate an intermittent gas pressure issue from the supply. An annual service that includes cleaning and inspecting the ignition components is the best way to prevent repeat lockouts. If your boiler has been serviced recently and the fault persists, ask the engineer to specifically test electrode gap and ionisation current under load.