Ariston boiler fault codes: what each code means
The two Ariston codes you are most likely to see are 108, which means the boiler needs filling, and 501, which means no flame was detected. Here is what each code in the Ariston Alteas ONE Net user's manual means, the checks you can safely do yourself, and the ones that need a Gas Safe registered engineer.
What do Ariston fault codes mean?
An Ariston fault code names the part of the boiler that stopped it running, and in this manual the numbering groups by area. The 1xx codes cover the central heating circuit and system water pressure, 3xx covers the circuit board, and 5xx covers ignition and flame detection. So 108 is a water pressure problem, 305 is a circuit board problem, and 501 is a gas and ignition problem.
Ariston splits the stoppages into two kinds, and the difference matters when you are deciding what to do. A safety shut-off is described in the manual as volatile, which means the boiler starts up again by itself as soon as the problem that caused it is removed. A lockout stays put until you press the RESET button on the control panel, and the display then shows Reset in progress followed by Fault solved. If a lockout comes back after several reset attempts, Ariston's instruction is to contact a qualified technician.
Every code on this page comes from one document that we opened and read: the Ariston Alteas ONE Net user's manual for Great Britain and Ireland. It carries an operation shutdown error table, plus three faults explained in the body of the manual. We have not listed any code we could not read in an Ariston manual ourselves, so this is not a complete list of every code Ariston uses.
This list covers the Alteas ONE Net. If you have a different Ariston boiler, or your code is not in the table below, check the manual for your exact model or ask a Gas Safe registered engineer before acting on it.
Ariston fault codes from the Alteas ONE Net manual
| Code | What Ariston calls it | Likely cause | DIY or engineer? |
|---|---|---|---|
| 101 | Overheating. | The boiler has overheated, which usually means water is not circulating properly: a pump that is not running, an air lock, radiator valves shut, a blocked filter or a sludged heat exchanger. | Partly DIY. Check the pressure gauge reads about 1 bar cold and that radiator valves are open, then reset once. Repeat lockouts need an engineer. |
| 103 to 107 | Flow Check Failed. Ariston gives these five codes one shared description in its table. | Not enough water is moving through the primary circuit. Common causes are a seized or air-locked pump, closed valves, a blocked filter or heavy sludge. | Partly DIY. Check radiator valves are open and the pressure is correct. Diagnosing the pump or cleaning the system is engineer work. |
| 108 | Filling Needed. The display shows Fault 108 - Filling Needed, and the boiler stops on a safety shut-off for insufficient water pressure. | System pressure has dropped below the minimum the boiler needs, often after bleeding radiators, or because of a small leak or a failed expansion vessel. | DIY. This is the one code Ariston prints a homeowner procedure for. See the steps below. |
| 110 | Send Probe Damaged. Ariston uses this as its example of a safety shut-off, so the boiler restarts by itself once the cause is gone. | The central heating flow (send) temperature probe or its wiring has failed. | Engineer only. |
| 305, 306, 307 | PCB Fault. | The boiler's printed circuit board has failed. | Engineer only. |
| 501 | No flame detected. The display shows Fault 501 - No flame detected and asks you to press the Reset button. | The gas supply being off, an empty prepayment meter, a closed gas isolation valve, a failed ignition electrode, a blocked condensate pipe or a gas valve fault. | Partly DIY for the first-line gas checks below. Smell gas? Call 0800 111 999. If it locks out again, stop and book a Gas Safe registered engineer. |
Which Ariston codes can I safely act on myself?
Three groups are worth trying yourself before you book anyone: 108 (filling needed), 501 (no flame detected), and up to a point 101 with 103 to 107 (overheating and poor circulation). The rest of the table, 110 and 305 to 307, is a failed probe or a failed circuit board inside the casing, which is engineer territory.
108: Ariston's own filling procedure
108 is the one code Ariston writes a homeowner procedure for in the Alteas ONE Net user's manual. Follow it in this order.
1. Re-establish the correct pressure using the filling loop, which is positioned underneath the boiler.
2. Press the MODE button for 5 seconds. The display shows AIR PURGE ACTIVE.
3. When the pressure gauge indicates a pressure of 1 bar, close the filling valve and press the MODE button. The display returns to the normal view.
Ariston then adds a warning worth taking seriously. If you find yourself refilling on a frequent basis, switch the boiler off, put the external electric switch in the OFF position, shut off the gas valve and contact a qualified technician to check for any leaks of water. Repeated pressure loss means water is going somewhere.
501: stop if you smell gas, then check the gas supply
If you can smell gas, or your carbon monoxide alarm is sounding, do not reset the boiler and do not carry out any of the checks below. Open the windows, turn the gas off at the meter if it is safe to do so, do not smoke or use naked flames, leave the electrical switches alone, get everyone out of the property, then call the National Gas Emergency Service on 0800 111 999.
If there is no smell of gas, 501 means the burner tried to light and no flame was sensed. Confirm the gas supply is on, that other gas appliances in the house still work, and that a prepayment meter has credit. If all three are fine, press RESET once. If it locks out on 501 again, stop and book a Gas Safe registered engineer, because the next suspects are the ignition electrode, the condensate pipe and the gas valve, and all three are gas work.
Resetting: five presses in 15 minutes is the limit
Ariston sets a hard limit on resets. The manual states that for safety reasons the boiler will permit a maximum of 5 resets in 15 minutes, and that at the 6th attempt within that 15-minute period the boiler will shut down and may only be operated again after the electricity supply has been disconnected. In practice, reset once. If the same code comes straight back, repeated resets only hide a developing fault, and Ariston says to contact a qualified technician.
101 and 103 to 107: circulation checks
These all point at water not moving through the boiler properly. Open every radiator valve, check the pressure gauge reads around 1 bar when the system is cold, and reset once. If the code returns, the likely culprits are the pump, an air lock, a blocked filter or sludge, and all of those are engineer work.
When to call a Gas Safe registered engineer
Call an engineer for 110 and for 305 to 307, for any code that involves gas or flame, and for any code you have already checked that comes back after a single reset. Ariston's own instruction is the same: if the problem shows itself again after several attempts to reset the appliance, contact a qualified technician. Ariston boilers are gas appliances, and by law anyone carrying out gas work as a business must be on the Gas Safe Register. Everyone working on gas must be competent, so working on a gas appliance yourself is dangerous and is not something to attempt.
There is one more instruction in the manual worth repeating. If the boiler still shows a safety shut-off after the cause looks cleared, switch it off, put the external electric switch in the OFF position, shut off the gas valve and contact a qualified technician. If you ever smell gas, suspect fumes or your carbon monoxide alarm sounds, do not wait for an appointment. Open the windows, turn the gas off at the meter if it is safe to do so, do not smoke or use naked flames, leave the electrical switches alone, get everyone out of the property, then call the National Gas Emergency Service on 0800 111 999.
A failed probe or a circuit board is a parts-and-labour job rather than a ten-minute visit, so it is worth deciding in advance whether you would rather pay for repairs as they come or hold an ongoing plan.
If a code is on your display today, the route is a one-off repair, because a new cover plan will not cover a fault you are already having. One-off repair visits run Monday to Friday, 09:00 to 17:00, and are not covered by a workmanship guarantee.
Smart Plan is a service plan, not insurance, and it covers future breakdowns rather than a fault that is already showing. On the boiler and central heating module, parts and labour are included up to £500 in a 12-month period if your boiler is under 7 years old, or up to £200 if it is over 7. Those are annual limits shared across every fault in the period, so a bigger repair can cost more than the plan pays and you would cover the difference. A £95 call-out fee, paid in advance, applies in the cases set out in the plan terms, including your first 30 days, during which cover still applies. Cover-plan call-outs run Monday to Friday, 08:00 to 18:00, with an engineer attending outside those hours only for a genuine emergency breakdown as defined in the plan terms, and we aim to get an engineer out within two working days. Once you use a service, a 12-month agreement period begins, and leaving early costs the remaining months or 75% of the outstanding balance. A 14-day cooling-off period applies and ends as soon as a service is used. We work with a national network of thousands of Gas Safe registered engineers. Smart Plan is from UK Boiler Company Ltd, trading since 2014. To book a one-off repair or talk through cover, call 0333 772 6247, Monday to Friday, 08:00 to 18:00.
Ariston fault code FAQs
What does 108 mean on an Ariston boiler?
Ariston calls 108 Filling Needed, and it is a safety shut-off caused by insufficient water pressure in the heating circuit. The manufacturer's procedure is to repressurise using the filling loop underneath the boiler, hold the MODE button for 5 seconds until AIR PURGE ACTIVE shows, then close the filling valve and press MODE once the gauge reads 1 bar. If you have to do this on a frequent basis, Ariston says to switch the boiler off, shut off the gas valve and have a qualified technician check for water leaks.
What does 501 mean on an Ariston boiler?
It means no flame was detected, so the burner tried to light and failed, and the display asks you to press the Reset button. If you can smell gas, do not reset it: leave the property and call 0800 111 999. Otherwise check the gas is on, that other gas appliances work and that a prepayment meter has credit, then reset once. If it locks out again, book a Gas Safe registered engineer, because the remaining suspects are the ignition electrode, a blocked condensate pipe and the gas valve.
What does Flow Check Failed mean on an Ariston boiler?
It is the description Ariston gives to codes 103, 104, 105, 106 and 107 together, and it means the boiler is not seeing enough water moving through its primary circuit. Open every radiator valve and check the pressure gauge reads about 1 bar cold. If the code comes back, the pump, an air lock, a blocked filter or sludge in the system are the usual reasons, and each of those needs an engineer.
How many times can I reset an Ariston boiler?
Five presses of the RESET button in 15 minutes. Ariston states that at the sixth attempt inside that window the boiler shuts down and can only be operated again once the electricity supply has been disconnected. In practice, reset once. If the fault returns immediately, the manufacturer's advice is to contact a qualified technician rather than keep resetting.
What is the difference between a safety shut-off and a lockout on an Ariston boiler?
A safety shut-off is what Ariston calls volatile: the boiler restarts by itself the moment the cause disappears, and 110 Send Probe Damaged is the example the manual uses. A lockout stays until you press RESET on the control panel, after which the display shows Reset in progress and then Fault solved. Either way, a fault that keeps returning needs a qualified technician rather than another reset.
My Ariston code is not on this list. What should I do?
This page only lists codes we could read in the Ariston Alteas ONE Net user's manual, so it is not every code Ariston uses across its ranges. Rather than guess at a meaning, check the manual for your exact model, or book a Gas Safe registered engineer to read the fault off the boiler. Guessing at a fault code on a gas appliance is not worth the risk.
Would a Smart Plan cover an Ariston fault that is already showing?
No. Cover is for future breakdowns, so a fault your boiler is showing today counts as pre-existing and is not covered. For a code on the display now, book a one-off repair. A plan protects against the next fault, with parts and labour up to £500 in a 12-month period if your boiler is under 7 years old or £200 if it is over 7, a £95 call-out fee paid in advance in set cases, and a 12-month agreement period once you use a service.
Ariston code still showing after the safe checks?
Book a one-off repair, Monday to Friday, 09:00 to 17:00, with no workmanship guarantee, and we aim to get a Gas Safe registered engineer out to diagnose it. Or set up a Smart Plan boiler and central heating module for future breakdowns, remembering it will not cover a code that is already showing today. A service plan, not insurance: parts and labour up to your cover limit of £500 in a 12-month period under 7 years or £200 over 7, shared across every fault in the period. Cover-plan call-outs run Monday to Friday, 08:00 to 18:00, with an engineer attending outside those hours only for a genuine emergency breakdown as defined in the plan terms. A £95 call-out fee, paid in advance, applies in set cases including your first 30 days, and using a service starts a 12-month agreement period, with early exit costing the remaining months or 75% of the outstanding balance.
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