The 501 fault code appears on 3 boiler brands — Ariston, ATAG and Chaffoteaux — and on all of them it points to the same kind of problem. The details still differ by brand (thresholds, sub-codes, reset procedure), so use the table below to jump to the page for your boiler.
The brand is printed on the front casing. Tap your brand for the full causes, fixes and repair costs.
| Brand | What 501 means | Severity | DIY? |
|---|---|---|---|
A Ariston | Fault code 501 on an Ariston boiler means the boiler attempted to light the burner but received no confirmation that a flame was established. Full guide → | Lockout — engineer likely | No |
A ATAG | Fault code 501 on an ATAG boiler means the appliance has tried to ignite and establish a flame multiple times — typically five consecutive attempts — but the ionisation (flame-sensing)… Full guide → | Lockout — engineer likely | No |
C Chaffoteaux | Fault code 501 (shown on the display as 'Err501' alongside the 'R' symbol) means the boiler attempted to fire but could not detect a flame via its ionisation circuit. Full guide → | Lockout — engineer likely | No |
Fault code 501 on an Ariston boiler means the boiler attempted to light the burner but received no confirmation that a flame was established. As a safety measure, the boiler immediately locks out and shuts down, leaving you without heating or hot water until the underlying problem is resolved. On some older Ariston models you may see this displayed as SP1 or 5P1 rather than 501 — the cause and remedy are the same.
Fault code 501 on an ATAG boiler means the appliance has tried to ignite and establish a flame multiple times — typically five consecutive attempts — but the ionisation (flame-sensing) circuit has not confirmed a stable flame at any point. The boiler then locks out as a safety measure. The root of the problem is almost always either a failure to produce a flame in the first place (ignition or gas supply issue) or a failure to detect one that is actually present (ionisation sensor or wiring fault). In cold weather, a frozen condensate pipe can also trigger this exact code by disrupting the boiler's operation before ignition completes.
Fault code 501 (shown on the display as 'Err501' alongside the 'R' symbol) means the boiler attempted to fire but could not detect a flame via its ionisation circuit. In plain terms, the burner either failed to light or the flame was detected as absent during normal operation. As a safety measure, the boiler enters a latching lockout — it will not attempt to restart on its own. You must press the RESET button on the front panel to clear it. Until the underlying cause is resolved, the boiler will produce neither heating nor hot water. This is the single most frequently seen fault code on Chaffoteaux boilers, so there is a well-established list of likely causes to work through.
Causes, fixes & costs for Chaffoteaux 501 → · All Chaffoteaux codes
Broadly, yes — on Ariston, ATAG and Chaffoteaux the 501 code points to the same class of fault, and the recommended response is similar. Model-specific details such as sub-codes and reset procedures still vary, so follow the page for your own brand.
Not usually. On every brand listed, 501 points to a fault that needs a suitably registered engineer to diagnose and repair. A single reset to rule out a transient glitch is reasonable; repeated resets are not.
For gas boilers, a Gas Safe registered engineer — it is a legal requirement for any work on the appliance. If you smell gas at any point, leave the property and call the National Gas Emergency line on 0800 111 999.
General guidance only — not a substitute for professional advice, and not certified by a registered engineer. Any work on a gas appliance must be carried out by a Gas Safe registered engineer. If you smell gas, call 0800 111 999.
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