The 108 fault code appears on 3 brands — Ariston, ATAG and Chaffoteaux — and it does not mean the same thing on each. The same two or three characters can signal a pressure problem on one boiler and an ignition fault on another, so identify your brand first and use the table below to jump to the right page.
The brand is printed on the front casing. Tap your brand for the full causes, fixes and repair costs.
| Brand | What 108 means | Severity | DIY? |
|---|---|---|---|
A Ariston | Fault code 108 on an Ariston boiler indicates that the water pressure inside the central heating circuit has fallen below the minimum operating threshold. Full guide → | Lockout — engineer likely | Some checks |
A ATAG | Fault code 108 on an ATAG boiler — sometimes displayed as 1P4 or F1P4 — signals that the water pressure inside the central heating system has dropped below the minimum acceptable threshold… Full guide → | Engineer may be needed | Some checks |
C Chaffoteaux | Fault code 108 on a Chaffoteaux boiler indicates that the water pressure in the central heating circuit has dropped below the minimum safe operating threshold. Full guide → | Lockout — engineer likely | Some checks |
Fault code 108 on an Ariston boiler indicates that the water pressure inside the central heating circuit has fallen below the minimum operating threshold. The boiler will stop functioning and lock out until the pressure is restored to a safe working level, typically between 1.0 and 1.5 bar. This is one of the most frequently seen Ariston fault codes and, in many cases, can be resolved by the homeowner without calling an engineer.
Fault code 108 on an ATAG boiler — sometimes displayed as 1P4 or F1P4 — signals that the water pressure inside the central heating system has dropped below the minimum acceptable threshold of approximately 0.8 bar. When pressure falls this low, the boiler's internal safety logic prevents it from firing in order to protect the heat exchanger and pump from running dry. You may notice the pressure gauge sitting well below the normal operating range of 1.0–1.5 bar. Restoring the pressure via the filling loop is often all that is needed, but if pressure keeps falling back down, there is likely an underlying fault requiring a Gas Safe engineer.
Fault code 108 on a Chaffoteaux boiler indicates that the water pressure in the central heating circuit has dropped below the minimum safe operating threshold. The boiler shuts down as a protective measure to prevent damage from running dry. You may also see this displayed as 1P4 or F1P4 on some Chaffoteaux models — these all point to the same underlying issue. Because Chaffoteaux sits within the Ariston Thermo group, this code appears across several Ariston-family boilers under equivalent fault descriptions. Normal operating pressure when the system is cold should sit between 1.0 and 1.5 bar; anything below roughly 0.5–0.8 bar will typically trigger this fault.
Causes, fixes & costs for Chaffoteaux 108 → · All Chaffoteaux codes
No. 108 means different things on different brands — see the table above. Always identify your boiler's brand (it is printed on the front casing) before acting on any advice about the code.
On some brands there are safe homeowner checks first — typically system pressure, the condensate pipe in cold weather, and a single reset. Where the code is a simple pressure or reset condition, that may be all it needs. Never open the boiler casing yourself.
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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