Andrews A10 Fault Code: Causes, Fixes & Repair Costs
What does the Andrews A10 fault code mean?
The A10 fault code on Andrews water heaters indicates that the appliance has attempted to light the burner but failed to establish or maintain a flame within the expected time window. As a safety measure, the unit shuts itself down — a state known as lockout — to prevent unburned gas from accumulating. Andrews water heaters are commercial-grade appliances manufactured by A.O. Smith, and while A10 is consistently reported by UK heating professionals as a flame failure or ignition lockout code, the precise trigger conditions can vary slightly between models. Always cross-reference with the manual for your specific Andrews unit.
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
- Gas supply interrupted or insufficient Common
If the gas meter has run out of credit (prepayment), a valve has been inadvertently closed, or there is a wider supply interruption in the street, the burner will have no fuel to ignite and A10 will be triggered. Check that other gas appliances such as a hob or oven are working normally.
- Dirty or degraded flame detection electrode Common
The flame sensor — sometimes called an ionisation probe — reads a small electrical signal produced by the burner flame. Carbon deposits, oxidation, or physical wear on the electrode tip reduce that signal, causing the control board to conclude no flame is present even when ignition has occurred.
- Worn or damaged spark electrode Common
The spark electrode produces the electrical arc that lights the gas. Over time the ceramic insulator can crack, the tip can erode, or the gap can widen beyond specification. Any of these faults prevent a reliable spark and result in repeated failed ignition attempts before the unit locks out.
- Faulty or seized gas valve Sometimes
The gas valve controls the flow of gas to the burner. If it fails to open fully — due to an internal fault, a wiring issue, or scale and debris — insufficient gas reaches the burner and ignition fails. Conversely, a valve stuck slightly open can cause unsafe conditions; either scenario triggers lockout.
- Blocked or restricted flue Sometimes
Andrews commercial water heaters rely on a clear flue path for safe combustion. A blockage caused by debris, bird nesting material, or a damaged flue terminal restricts the exhaust gases, disrupts the air-to-gas ratio, and can prevent a stable flame from forming.
- Faulty ignition lead or wiring fault Sometimes
The high-voltage lead connecting the PCB to the spark electrode can degrade, develop cracks in the insulation, or work loose at either end. A poor connection means the spark energy is lost before it reaches the electrode tip, resulting in no ignition.
- PCB or ignition module failure Rare
The printed circuit board manages the entire ignition sequence — fan pre-purge, gas valve opening, spark timing, and flame confirmation. A fault on the board can cause the sequence to abort at any stage, producing an A10 code even when every other component is in good condition.
How to fix it
- Check the gas supply to the property DIY safe
Turn on a gas hob ring or check another gas appliance. If nothing works, the issue is upstream of the water heater — contact your gas supplier or check your meter credit before doing anything else.
- Reset the water heater once DIY safe
Locate the reset button or procedure described in your Andrews model's user guide (often a button on the control panel). Press and hold as instructed. If the unit lights and runs normally, monitor it over the next hour. Do not reset more than two or three times in total — repeated resets on a locked-out appliance can mask a serious fault.
- Check system pressure if applicable DIY safe
Some Andrews models are connected to sealed heating circuits. If a pressure gauge is visible and reads below 1 bar, top up via the filling loop following the instructions in your user manual. Low pressure alone is unlikely to cause A10, but it is worth ruling out.
- Inspect the flue terminal externally DIY safe
From outside the building, visually check that the flue outlet is not obviously blocked by debris, ice, or a bird nest. Do not attempt to dismantle any flue components — if you suspect an internal blockage, this must be investigated by an engineer.
- Have a Gas Safe engineer inspect and clean the flame detection electrode Gas Safe engineer
An engineer will remove the burner access cover, examine the ionisation probe or flame sensor for carbon fouling or physical damage, clean it with fine abrasive if appropriate, and retest ignition. This is one of the most common resolutions for A10.
- Have the spark electrode and ignition lead tested and replaced if necessary Gas Safe engineer
The engineer will check the electrode gap, inspect the ceramic insulator for cracks, test the high-voltage lead for continuity and insulation breakdown, and replace whichever components fall outside manufacturer tolerances.
- Have the gas valve tested Gas Safe engineer
Using a manometer and the manufacturer's commissioning procedure, the engineer will verify that the gas valve opens to deliver the correct inlet and burner pressures. A valve that is out of specification or failing electrically will be replaced.
- Have the flue system inspected internally Gas Safe engineer
The engineer will check the entire flue run for blockages, incorrect fall, or damage, and verify that the fan (where fitted) is delivering the correct air flow for combustion. A blocked or poorly drawing flue is a safety hazard as well as a cause of flame failure.
- Have the PCB or ignition module assessed Gas Safe engineer
If all gas-side and ignition components test satisfactorily, the engineer will turn attention to the control board. PCB faults can be intermittent and require specialist test equipment to confirm before an expensive replacement is committed to.
- Call a Gas Safe registered engineer if the fault persists Gas Safe engineer
If you have reset the unit and confirmed the gas supply is live but A10 returns, do not continue resetting. Contact a Gas Safe registered engineer experienced with commercial Andrews or A.O. Smith water heaters. You can find registered engineers at GasSafeRegister.co.uk.
Parts you may need
- Flame detection / ionisation electrode · from £35
- Spark electrode assembly · from £45
- Ignition lead (HT lead) · from £25
- Gas valve · from £220
- Ignition control module · from £95
- PCB (control board) · from £290
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
Is it safe to keep resetting an Andrews water heater showing A10?
No. One or two resets is reasonable to clear a transient fault, but A10 is a safety lockout triggered because the appliance could not confirm a stable flame. Resetting repeatedly without identifying the cause risks allowing unburned gas into the flue or combustion chamber. If the code returns after a couple of resets, stop and call a Gas Safe registered engineer.
Could a blocked condensate pipe cause an A10 fault on an Andrews unit?
It is unlikely. A10 specifically relates to flame failure rather than flue gas temperature or condensate drainage. Andrews commercial water heaters that develop a condensate blockage typically display a different fault. If you are unsure which fault code your model is showing, consult the model-specific manual or contact Andrews technical support.
How much does it cost to fix an Andrews A10 fault?
Most A10 repairs fall in the range of £120–£380. Cleaning or replacing an electrode and lead tends to sit at the lower end (around £120–£180 including labour), while a gas valve replacement typically runs £250–£380. A PCB replacement can push beyond this range — often £350–£550 or more on a commercial unit — but that outcome is less common. An engineer will usually be able to give you a firm quote once they have identified the faulty component.
Why does my Andrews water heater show A10 only first thing in the morning?
Cold-start ignition failures are often caused by a flame detection electrode that is borderline — it just about works once the unit has warmed up but struggles when everything is cold. Carbon fouling on the sensor tip, a marginally low gas pressure, or a cracked electrode insulator can all behave this way. An engineer should be able to replicate the fault on a cold start and then identify the root cause.