- Boilers
- Gas boiler
501
Ariston 501 on a gas boiler: no flame
Risk level
High
Professional inspection is recommended.
Urgency
High
Quick answer
Ariston 501 means there is no flame and the boiler has locked out for safety. Check the gas tap is open and press the reset button; if the lockout keeps happening, call Ariston's official service centre.
Safety first
Stop and check this first
- If you smell gas: Ariston says to close the main gas tap, open the windows and call the technician. Do not operate switches or light flames, leave the home and call your gas distributor's emergency number from outside. If you smell burning or see smoke, cut the power, close the gas and ventilate.
- Do not chain resets: Ariston limits them to 5 in 15 minutes. If 501 keeps returning, leave the boiler off with the gas closed and call the service centre. Do not open the boiler.
Safe checks you can perform
- Gas smell before resetting
- Gas tap and supply
- Reset with the reset button
- Ignition and flame check by the technician
Leave these tasks to a qualified professional
- Do not attempt this professional task: Ignition and ionisation current check
- Do not attempt this professional task: Combustion analysis
- Do not attempt this professional task: Gas pressure measurement at the boiler
What a technician must be able to justify
Technician visit
These are the steps they must carry out and show you. Tick them as they work: if steps are skipped, do not accept a part swap.
These are not instructions for opening or handling the equipment yourself. They are the checks that should support a technical conclusion.
Ignition and ionisation current check
What they doThe technician checks ignition and measures the flame detection signal.
They must show youthe flame signal reading.
In writingwhich part was cleaned or replaced and why.
Combustion analysis
What they doThe technician measures CO2 or O2 and CO with an analyser and adjusts if needed.
They must show youthe analyser printout.
In writingthe values in the installation log.
Gas pressure measurement at the boiler
What they doThe technician measures gas pressure at the boiler's test point with the burner running and compares it with Ariston's specification.
They must show youthe measured value against the specification.
In writingthe pressure measured and whether it was a supply problem.
Before accepting a part or repair
Nothing has been shown yet. Do not accept a part swap based on the code alone.
Follow these steps
Note: Follow the documented order. An error code identifies the affected system, but it does not prove by itself which part has failed.
Gas smell before resetting
- Who:
- you.
- How:
- without touching switches, notice whether it smells of gas near the boiler.
- Result that matters:
- whether there is a gas smell.
- If it smells of gas:
- do not reset; follow the gas warning on this page.
- If there is no smell:
- check the gas supply.
- Evidence to keep:
- a note of the time and what you noticed.
Evidence: Ariston CLAS One System, manual de usuario
Gas tap and supply
- Who:
- you.
- How:
- check the boiler's gas tap is open and whether the hob or another gas appliance works.
- Result that matters:
- whether gas reaches the boiler.
- If the tap was closed or there is no gas at home:
- open the tap or contact your distributor; Ariston lists lack of gas as a cause.
- If there is gas:
- the cause is in ignition or the flame.
- Evidence to keep:
- a photo of the gas tap and a note of whether the hob worked.
Evidence: Calderas Ariston: significados de los códigos de error
Reset with the reset button
- Who:
- you.
- How:
- press the reset button on the panel, as Ariston says for non volatile errors. Do not exceed 5 resets in 15 minutes: on the sixth the boiler locks and can only be unlocked by disconnecting it.
- Result that matters:
- whether the boiler lights and keeps the flame.
- If it runs and the lockout is a one off:
- Ariston says it is not a problem; note the date.
- If 501 keeps returning:
- call Ariston's official service centre.
- Evidence to keep:
- a photo of the display with 501 and a note of each reset.
Evidence: Calderas Ariston: significados de los códigos de error · Ariston CLAS One System, manual de usuario
Ignition and flame check by the technician
- Who:
- authorised gas technician.
- How:
- checks gas pressure, ignition and flame detection, and analyses the combustion.
- Result that matters:
- whether gas is missing, ignition fails or the flame is unstable.
- If gas pressure is too low:
- it is a supply problem.
- If gas arrives properly:
- it points to ignition or flame detection.
- Evidence to keep:
- a report with the gas pressure measured and the repair.
Ariston reserves repairs for its official service centre or a qualified technician: opening the boiler is not the user's job.
Evidence: Calderas Ariston: significados de los códigos de error · Ariston CLAS One y CLAS One System, instrucciones técnicas para la instalación y el mantenimiento · Ariston CLAS One System, manual de usuario
Still not solved
If the error persists, stop here. See what the technician must do and show you.
Where this code applies
A code is meaningful only inside the right product and version context.
Primary scope
- System
- Boilers
- Brand
- Ariston
- Product type
- Gas boiler
Known code variants
- 5 01
- Ariston 5 01
- Ariston E501
- Chaffoteaux 5 01
- Clas One 501
- Error 501 Ariston
- Error 501 Chaffoteaux
- Pigma 501
What it means
In the Clas One code table, 5 01 is no flame, in the ignition and flame detection group. Ariston describes it as a non volatile error: the boiler does not recover by itself and must be restarted by hand. Ariston lists lack of gas, ignition failure or an unstable flame as possible causes. For safety the boiler allows at most 5 resets in 15 minutes. The code does not say whether gas is missing or ignition is failing.
Warnings and stop conditions
- Criticaleditorial warning
If you smell gas: Ariston says to close the main gas tap, open the windows and call the technician. Do not operate switches or light flames, leave the home and call your gas distributor's emergency number from outside. If you smell burning or see smoke, cut the power, close the gas and ventilate.
Evidence: Ariston CLAS One System, manual de usuario
- Highsource verified
Do not chain resets: Ariston limits them to 5 in 15 minutes. If 501 keeps returning, leave the boiler off with the gas closed and call the service centre. Do not open the boiler.
Evidence: Calderas Ariston: significados de los códigos de error · Ariston CLAS One System, manual de usuario
Symptoms and causes
Probable causes · in order
- No gasCommon
Ariston lists this first. It fits if the gas tap is closed, other gas appliances do not work either or there was a supply cut.
Evidence: Calderas Ariston: significados de los códigos de error
- Ignition failurePossible
If gas arrives and the boiler tries to light without success, the fault is in the ignition system; only the technician can check it.
Evidence: Calderas Ariston: significados de los códigos de error · Ariston CLAS One y CLAS One System, instrucciones técnicas para la instalación y el mantenimiento
- Unstable flamePossible
Ariston lists an unstable flame. It fits if the boiler lights and goes out shortly before locking out; a combustion analysis separates it.
Evidence: Calderas Ariston: significados de los códigos de error
Virtual technician
Does 501 still appear after these checks?
Answer a few questions to narrow down the likely cause and the safest next action. Guidance only - it never replaces a professional.
Sources and technical references
- 1
Calderas Ariston: significados de los códigos de error
Ariston · 2025 · official_doc
- 3
Ariston CLAS One System, manual de usuario
Ariston · 2017 · manual
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