E08 Boiler Fault Code: What It Means on Every Brand

The E08 fault code appears on 4 brands — Biasi, Johnson & Starley, Keston and Ravenheat — 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 E08 means	Severity	DIY?
BBiasi	The Biasi E08 (also displayed as ER 08) fault code indicates that the boiler's external NTC (Negative Temperature Coefficient) temperature probe has either failed, is producing readings… Full guide →	Engineer may be needed	No
JSJohnson & Starley	E08 on a Johnson & Starley unit reports a flame circuit failure: the electronics that detect and supervise the burner flame have failed their own integrity checks. Full guide →	Lockout — engineer likely	No
KKeston	The E08 code on a Keston boiler signals one of two closely related problems: a flame circuit error pointing to a possible control board (PCB) fault, or a flue overheat condition where the… Full guide →	Lockout — engineer likely	No
RRavenheat	The E08 fault code (also displayed as 08E on some Ravenheat models) indicates that the boiler has detected water pressure below its safe operating threshold — typically under 0.6 bar. Full guide →	Lockout — engineer likely	Some checks

E08 brand by brand

Biasi E08

The Biasi E08 (also displayed as ER 08) fault code indicates that the boiler's external NTC (Negative Temperature Coefficient) temperature probe has either failed, is producing readings outside the expected range, or has a wiring fault between the sensor and the PCB. NTC sensors are thermistors whose electrical resistance changes predictably with temperature — when the boiler's control board detects a reading that doesn't make sense, or gets no signal at all, it locks out and displays E08. This sensor is only present on systems set up for outdoor weather compensation; if your boiler's PCB is configured to expect an external sensor but none is physically connected, E08 can also appear for that reason.

Causes, fixes & costs for Biasi E08 → · All Biasi codes

Johnson & Starley E08

E08 on a Johnson & Starley unit reports a flame circuit failure: the electronics that detect and supervise the burner flame have failed their own integrity checks. This differs from a simple failed ignition — the controller is saying it cannot trust its flame-sensing circuit at all, so it will not run the burner under any circumstances until the circuit is proven. Causes concentrate in the flame electrode and its lead, their connections to the board, and the board's flame-amplifier stage itself. Because flame supervision is the core of gas-appliance safety, E08 is strictly an engineer's fault.

Causes, fixes & costs for Johnson & Starley E08 → · All Johnson & Starley codes

Keston E08

The E08 code on a Keston boiler signals one of two closely related problems: a flame circuit error pointing to a possible control board (PCB) fault, or a flue overheat condition where the temperature measured at the flue has climbed more than 10°C above the boiler's return water temperature. Either situation causes the boiler to lock out and stop firing until the underlying fault is resolved. Because Keston boilers use a twin-flue design with a modulating pump, E08 can sometimes involve both issues simultaneously — for example, a scaled heat exchanger causing flue overheating that the PCB then misinterprets as a flame circuit problem.

Causes, fixes & costs for Keston E08 → · All Keston codes

Ravenheat E08

The E08 fault code (also displayed as 08E on some Ravenheat models) indicates that the boiler has detected water pressure below its safe operating threshold — typically under 0.6 bar. Without sufficient pressure, the heat exchanger risks overheating, so the boiler locks out as a precaution. Homeowners usually notice that both heating and hot water have stopped working when this code appears. The fix may be as simple as topping up the system pressure, but a recurring fault points to an underlying problem such as a waterlogged expansion vessel, a weeping pressure relief valve, or a leak somewhere in the system.

Causes, fixes & costs for Ravenheat E08 → · All Ravenheat codes

Frequently asked questions

Is the E08 fault code the same on every boiler?

No. E08 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 E08 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 E08 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.