E133 Boiler Fault Code: What It Means on Every Brand

E133 is one of the most-searched boiler codes in the UK, and unusually it means the same thing on every brand that uses it — Baxi, Potterton, Main and Biasi all share the same control platform, so E133 is always an ignition or gas-supply lockout: the boiler tried to light, could not prove a flame, and shut down. On Potterton displays it often shows as 'E1' alternating with '33', which is why people search for 'E1 33'. The usual homeowner checks are the same across all four: is the gas on (other gas appliances working, prepayment meter in credit), and in winter, is the condensate pipe frozen? One reset after those checks is fine; a returning E133 needs a Gas Safe engineer.

Lockout — engineer likely 4 brands use this code

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 E133 means	Severity	DIY?
BBaxi	E133 on a Baxi boiler is a gas supply or ignition lockout: the boiler tried to light its burner, could not prove a flame within its ignition window, and shut down for safety. Full guide →	Lockout — engineer likely	Some checks
BBiasi	The E133 code (sometimes shown alongside a red lockout light as ER01 on older Biasi models) means your boiler made several attempts to ignite and failed to establish a flame it could… Full guide →	Lockout — engineer likely	Some checks
MMain	The E133 fault code on a Main boiler indicates that the boiler attempted to light but failed to establish a flame, causing it to shut down into safety lockout. Full guide →	Lockout — engineer likely	Some checks
PPotterton	The E133 code appears on Potterton boilers — often displayed as 'E1' alternating with '33' — when the boiler has attempted to ignite, failed to detect a stable flame, and shut itself down… Full guide →	Lockout — engineer likely	Some checks

E133 brand by brand

Baxi E133

E133 on a Baxi boiler is a gas supply or ignition lockout: the boiler tried to light its burner, could not prove a flame within its ignition window, and shut down for safety. It is by far the most common Baxi fault code — and the same code, with the same meaning, appears on Potterton and Main boilers (which share Baxi's control platform), where it is sometimes displayed as 'E1' alternating with '33'. Nine times out of ten in winter the cause is outside the boiler altogether: a frozen condensate pipe, or a gas supply that has stopped (empty prepayment meter, a tripped gas meter valve, or a supply interruption). The homeowner checks take five minutes and often fix it; if E133 comes straight back after one reset, it needs a Gas Safe registered engineer.

Causes, fixes & costs for Baxi E133 → · All Baxi codes

Biasi E133

The E133 code (sometimes shown alongside a red lockout light as ER01 on older Biasi models) means your boiler made several attempts to ignite and failed to establish a flame it could detect — so it has shut itself down as a safety precaution. Essentially, the boiler tried to light, something prevented it from doing so successfully, and it has locked out to stop any unsafe condition developing. You will have no heating or hot water until the underlying cause is resolved. Note on Biasi model variants: older models such as the Riva Plus and Garda display this type of ignition lockout as ER01 or ER02, while newer models including the Inovia and Advance Plus use the E-code format (E133, E110, E118). The fault and its causes are the same across all these variants — only the display wording differs.

Causes, fixes & costs for Biasi E133 → · All Biasi codes

Main E133

The E133 fault code on a Main boiler indicates that the boiler attempted to light but failed to establish a flame, causing it to shut down into safety lockout. Rather than continuing to run unsafely, the boiler stops all heating and hot water output until the underlying problem is resolved. You may hear repeated clicking as the boiler tries — and fails — to ignite before the lockout triggers. This same fault code also appears on Potterton boilers, which share a very similar ignition and gas control architecture with Main.

Causes, fixes & costs for Main E133 → · All Main codes

Potterton E133

The E133 code appears on Potterton boilers — often displayed as 'E1' alternating with '33' — when the boiler has attempted to ignite, failed to detect a stable flame, and shut itself down as a safety precaution. In plain terms, the boiler tried to light, couldn't confirm a flame was present, and locked out rather than continue operating unsafely. This code is also common on Baxi and Main boilers, which share closely related ignition and gas control systems.

Causes, fixes & costs for Potterton E133 → · All Potterton codes

Frequently asked questions

Is the E133 fault code the same on every boiler?

Broadly, yes — on Baxi, Biasi, Main and Potterton the E133 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.

Can I fix a E133 fault myself?

On some brands there are safe homeowner checks first — typically system pressure, the condensate pipe in cold weather, and a single reset. The underlying repair usually needs a registered engineer. Never open the boiler casing yourself.

Who should I call about a E133 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.