E118 Boiler Fault Code: What It Means on Every Brand

The E118 fault code appears on 4 brands — Baxi, Biasi, Main and Potterton — 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.

Up to: Lockout — engineer likely 4 brands use this code Meaning differs by brand

Which brand is your boiler?

The brand is printed on the front casing. Tap your brand for the full causes, fixes and repair costs.

Brand	What E118 means	Severity	DIY?
BBaxi	The E118 code appears on Baxi boilers when the central heating system pressure has fallen to 0.5 bar or below — well beneath the minimum needed for safe operation. Full guide →	Lockout — engineer likely	Some checks
BBiasi	The E118 fault code appears on newer Biasi boiler models — including the Inovia and Advance Plus — and signals that the system water pressure has fallen critically low, typically below 0.5… Full guide →	Lockout — engineer likely	Some checks
MMain	The E118 code appears on Main boilers (and the closely related Baxi and Potterton ranges, which share the same fault code system under the BDR Thermea group) when the system water pressure… Full guide →	Engineer may be needed	Some checks
PPotterton	The E118 code on a Potterton boiler indicates that the central heating system pressure has fallen to a level too low for the boiler to operate safely — specifically below 0.5 bar, at which… Full guide →	Lockout — engineer likely	Some checks

E118 brand by brand

Baxi E118

The E118 code appears on Baxi boilers when the central heating system pressure has fallen to 0.5 bar or below — well beneath the minimum needed for safe operation. At this point the boiler locks out automatically to prevent damage to the heat exchanger and pump. The boiler will not fire or provide hot water until adequate pressure is restored and the unit is reset. In most cases the fix is straightforward: repressurise via the filling loop and reset. However, if pressure drops repeatedly, an underlying leak or a failing component is almost certainly to blame and a Gas Safe engineer should investigate.

Causes, fixes & costs for Baxi E118 → · All Baxi codes

Biasi E118

The E118 fault code appears on newer Biasi boiler models — including the Inovia and Advance Plus — and signals that the system water pressure has fallen critically low, typically below 0.5 bar. At this point the boiler's safety controls kick in and shut the unit down entirely, so you'll lose both heating and hot water until the pressure is restored and the fault is cleared. On older Biasi ranges such as the Riva Plus and Garda you may see an equivalent ER-series code instead, but the underlying issue and the steps to resolve it are identical. A sealed central heating system relies on a specific pressure range to circulate water properly; when that pressure collapses, the boiler simply cannot do its job safely.

Causes, fixes & costs for Biasi E118 → · All Biasi codes

Main E118

The E118 code appears on Main boilers (and the closely related Baxi and Potterton ranges, which share the same fault code system under the BDR Thermea group) when the system water pressure drops below 1 bar. At that point the boiler locks out to protect itself from running without adequate water circulation. Normal operating pressure should sit between 1.0 and 1.5 bar when the system is cold. The E118 fault is not an immediate safety emergency, but leaving it unaddressed can lead to component wear and repeated lockouts. In most cases, topping up the pressure via the filling loop clears the fault — though a recurring drop points to an underlying problem that needs professional attention.

Causes, fixes & costs for Main E118 → · All Main codes

Potterton E118

The E118 code on a Potterton boiler indicates that the central heating system pressure has fallen to a level too low for the boiler to operate safely — specifically below 0.5 bar, at which point the boiler locks out to protect itself and the wider system. In practice, you may notice the fault appearing even before reaching that threshold, as pressure between 0.5 and 1.0 bar is already too low for reliable operation. Most Potterton boilers need to sit between 1.0 and 1.5 bar when cold to function correctly. Until pressure is restored to a safe level, the boiler will not fire, leaving you without heating or hot water.

Causes, fixes & costs for Potterton E118 → · All Potterton codes

Frequently asked questions

Is the E118 fault code the same on every boiler?

No. E118 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.

Can I fix a E118 fault myself?

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.

Who should I call about a E118 fault?

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.