Ariston 501 fault codewhat it means and how to fix it
No flame was detected during ignition and the appliance has locked out. Check the gas supply and the condensate pipe before booking anyone.
Take care
What 501 means
The 5 at the front tells you this is the ignition and detection group, and Ariston's own words for 501 are "no flame detected". It is the shutdown that follows repeated failed attempts to establish one. Ariston distinguish it from the warnings that precede it: 5P1 is the first ignition attempt unsuccessful, 5P2 and 5P3 the ones after it, and 5P6 an ignition-failed warning. By the time you see 501 the appliance has given up.
Ariston describe this as a non-volatile shutdown, meaning it will not clear itself and needs a manual reset. What the code cannot tell you is why the flame never appeared. Four causes account for almost all of them, and helpfully the two most common are things you can investigate yourself: no gas actually reaching the appliance, and a condensate drain frozen solid outside. The other two, a worn ignition electrode and a gas valve fault, need an engineer.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Frozen condensate pipe | The plastic drain outside ices up and condensate backs into the appliance within a minute of firing. Dominates this fault in cold weather. | Common |
| Gas supply interrupted | Prepayment meter out of credit, the emergency control valve knocked shut, or a genuine supply problem. Test it by trying a gas hob. | Common |
| Ignition electrode worn | A consumable part. The tip erodes over years until the spark is too weak to light the burner dependably. | Occasional |
| Gas valve fault | Not opening, or not delivering a stable enough rate to establish a flame. The dearest possibility and the rarest. | Rare |
What to try yourself
Light a gas hob ring. If it will not light either, the gas supply is the problem and the boiler is doing exactly what it should.
If you are on a prepayment meter, check the credit including any emergency credit that may have run out overnight.
Outside, trace the white or grey plastic condensate pipe down from the appliance and feel along it for a solid, ice-cold length — the bends and the open end freeze first.
Thaw any ice with hand-hot water poured slowly along the pipe. Boil a kettle and let it stand ten minutes so it is hot but not scalding.
Never use boiling water, a heat gun, or any naked flame. Cracking a cold plastic pipe turns a free repair into a plumbing job in the worst possible weather.Press reset once. If the appliance lights and holds, the condensate was the cause — get the external run lagged before next winter.
Get a Gas Safe registered engineer to look at your Ariston 501
We do not pass enquiries to a repair firm, so there is no form here. Find a Gas Safe registered engineer through the Gas Safe Register, and ask to see their registration card when they arrive — it is the register, not the van, that tells you they are qualified.
What it costs to fix
Typical repair cost
£0–£320
Time on site
25 minutes
Nothing if it is a frozen condensate pipe you clear yourself. An ignition electrode is £110 to £190 fitted; a gas valve £240 to £320.
Typical UK prices including parts and labour, updated September 2026. Your quote may differ.
Parts you may need
We may earn a commission if you buy a part through one of these links. It does not change what you pay, and it does not affect which parts we list.
Condensate trap and siphon
COND-TRAP£15–£38Plumbing merchant
Price checked 28 September 2026
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Related Ariston fault codes
- 303Get it checkedThe main control board has reported an internal fault. It needs an engineer, and it is worth checking the electrical supply before assuming the board is dead.Related: ignition and gas supply
- 108Usually simple to fixThe heating circuit does not contain enough water to run safely. Refill through the filling loop to about 1.2 bar and the code clears.Related: same brand
- 101Get it checkedThe heating circuit has overheated and the appliance has shut down. The usual reason is that water has stopped moving, not that it is firing too hard.Related: same brand
- 103Get it checkedThe appliance is reporting insufficient circulation — water is not moving through it fast enough. Worth acting on before it becomes an overheat.Related: same brand
- 604Get it checkedFan speed is outside the range the appliance expects, so it will not allow the burner to light. This one needs an engineer.Related: same brand
- 109Get it checkedSystem pressure has gone above 3 bar. Usually this means somebody overfilled it, or the expansion vessel has failed.Related: same brand
Own an Ariston boiler? Save it and its codes come first next time.
Related guides
Common questions about Ariston 501
What is the difference between 501 and 5P1?
5P1 is a warning logged after a single failed ignition attempt while the appliance is still trying. 501 is the lockout it reaches after repeated failures. Seeing 5P1 in the error list after the appliance recovered is normal history; seeing 501 on the display means it has stopped.
The display says I have used all my resets. What now?
You have hit the limit Ariston publish — five presses of RESET in fifteen minutes, after which the boiler shows 304, too many resets in fifteen minutes. Ariston do not spell out in the manuals we could read what clears that, and it does not matter much, because the answer at that point is an engineer rather than a way of getting more attempts. Five failed ignitions have already told you the appliance cannot light.
What is 502, and is it the same thing?
The opposite, and it is more serious. Ariston define 502 as flame detected with the gas valve closed. Rather than failing to light, the appliance is reporting a flame at a point where there should not be one, which can mean a gas valve that is not sealing. Do not keep resetting that one — isolate the boiler at the fused spur and get a Gas Safe engineer to it.
Could a blocked flue cause this?
Yes. A blocked or badly positioned flue terminal prevents clean combustion and produces the same lockout. Have a look at the terminal from outside while you are checking the condensate pipe — nests and render splashes are both common.
Technical review
Not reviewed by an engineer
No engineer has read this page. Severity follows what the manufacturer publishes, and we would rather tell you that than let a byline imply a sign-off.
Sources and how we verified this
We establish the facts from the sources below and then write the explanation ourselves. We do not copy manufacturer wording and we do not host their manuals.
- Manufacturer technical and service documentation
- Manufacturer support portal
- Trade body guidance
This page has not been reviewed by an engineer, and we would rather tell you that than imply otherwise. The severity rating follows what the manufacturer publishes: where they say isolate the appliance and call someone, so do we.