E01 Boiler Fault Code: What It Means on Every Brand

The E01 fault code appears on 4 brands — Biasi, Johnson & Starley, Keston and Warmflow — 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 E01 means	Severity	DIY?
BBiasi	The Biasi E01 (also displayed as ER 01 on older models such as the Riva Plus and Garda, or E133 on newer Inovia and Advance Plus models) indicates that the boiler has failed to ignite and… Full guide →	Lockout — engineer likely	No
JSJohnson & Starley	The E01 code appears on Johnson & Starley boilers when the burner has failed to establish a flame after three consecutive ignition attempts. Full guide →	Lockout — engineer likely	No
KKeston	The E01 code appears on Keston C36 boilers (note: the equivalent fault on C40 and C55 models is E02) when the boiler has made five consecutive attempts to light the burner without success. Full guide →	Lockout — engineer likely	Some checks
WWarmflow	The E01 code on a Warmflow boiler signals a burner lockout — a built-in safety shutdown that occurs when the boiler cannot establish or maintain a flame during start-up or normal operation. Full guide →	Lockout — engineer likely	No

E01 brand by brand

Biasi E01

The Biasi E01 (also displayed as ER 01 on older models such as the Riva Plus and Garda, or E133 on newer Inovia and Advance Plus models) indicates that the boiler has failed to ignite and has locked itself out as a safety measure. Essentially, the burner attempted to light but could not establish or sustain a flame, so the boiler has shut down to prevent unburned gas from accumulating. Depending on the model, this code can also flag a low system pressure condition, since some Biasi control boards will refuse to attempt ignition if pressure has dropped too far. In either case, the boiler will not produce heat or hot water until the underlying problem is resolved and the unit is reset.

Causes, fixes & costs for Biasi E01 → · All Biasi codes

Johnson & Starley E01

The E01 code appears on Johnson & Starley boilers when the burner has failed to establish a flame after three consecutive ignition attempts. At that point the boiler shuts itself down — a condition known as ignition lockout — and holds the fault code on the display until the underlying problem is resolved and the unit is reset. The boiler is protecting itself and your home: running a burner that can't detect a proper flame would be unsafe. Common triggers range from something as simple as a temporary interruption to the gas supply, through to worn ignition or flame-sensing electrodes, a faulty gas valve, a blocked condensate siphon, or — in rarer intermittent cases — a failing PCB or, on Warmcair models, the ESYS ignition control module mounted on the gas valve.

Causes, fixes & costs for Johnson & Starley E01 → · All Johnson & Starley codes

Keston E01

The E01 code appears on Keston C36 boilers (note: the equivalent fault on C40 and C55 models is E02) when the boiler has made five consecutive attempts to light the burner without success. Rather than continuing to try indefinitely, the boiler enters a hard lockout to protect itself and your home. You must press the reset button on the control panel to clear the lockout — simply switching the boiler off and on at the mains will not work.

Causes, fixes & costs for Keston E01 → · All Keston codes

Warmflow E01

The E01 code on a Warmflow boiler signals a burner lockout — a built-in safety shutdown that occurs when the boiler cannot establish or maintain a flame during start-up or normal operation. Once triggered, the boiler stops firing to prevent unsafe conditions such as unburnt fuel accumulating in the combustion chamber. On older or non-Agentis Warmflow models that lack a digital display, this same condition is typically indicated by a glowing red reset light on the burner unit rather than a text code. Because Warmflow boilers run on oil, the registered trade for repairs is OFTEC (not Gas Safe), though many engineers hold both registrations.

Causes, fixes & costs for Warmflow E01 → · All Warmflow codes

Frequently asked questions

Is the E01 fault code the same on every boiler?

No. E01 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 E01 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 E01 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.