5 Boiler Fault Code: What It Means on Every Brand

The 5 fault code appears on 3 brands — Halstead, Intergas and Johnson & Starley — 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 3 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 5 means	Severity	DIY?
HHalstead	Fault code 5 on Halstead boilers points to a problem with one or more of the boiler's temperature sensors (NTC thermistors) or, on Ace HE models, a blown thermal fuse. Full guide →	Engineer may be needed	No
IIntergas	Intergas fault code 5 tells you that the boiler's flame sensor is picking up a signal that is weaker than expected — not necessarily no flame at all, but one that isn't strong enough to… Full guide →	Lockout — engineer likely	No
JSJohnson & Starley	Fault Code 5 on Johnson & Starley appliances — displayed as 'E5' on WarmCair warm air heaters and related models such as the Economaire, QuanTec, and Reno ranges — indicates that the… Full guide →	Lockout — engineer likely	No

5 brand by brand

Halstead 5

Fault code 5 on Halstead boilers points to a problem with one or more of the boiler's temperature sensors (NTC thermistors) or, on Ace HE models, a blown thermal fuse. The exact interpretation varies slightly by model range. On Eden VBX series boilers the display shows fault 5 when the flow sensor, return sensor, or flue gas sensor is giving the PCB a bad reading — or when the wiring and connectors to those sensors (typically PCB connectors X6 and X8) have developed a fault. On Ace HE series boilers the same LED code indicates a defective sensor or a blown thermal fuse, again resulting in the boiler failing to establish or maintain a flame. In both cases the boiler's control board is not receiving the temperature data it needs to operate safely, so it shuts down. A typical symptom is the boiler firing up, running for five to ten minutes, then cutting out — sometimes repeating this cycle before displaying the fault.

Causes, fixes & costs for Halstead 5 → · All Halstead codes

Intergas 5

Intergas fault code 5 tells you that the boiler's flame sensor is picking up a signal that is weaker than expected — not necessarily no flame at all, but one that isn't strong enough to satisfy the boiler's safety parameters. As a precaution, the boiler locks itself out to prevent the risk of incomplete combustion or harmful gases building up. The underlying cause can range from a straightforward gas supply issue through to a faulty internal component, so a Gas Safe registered engineer will need to diagnose and resolve the fault before the boiler can return to normal operation.

Causes, fixes & costs for Intergas 5 → · All Intergas codes

Johnson & Starley 5

Fault Code 5 on Johnson & Starley appliances — displayed as 'E5' on WarmCair warm air heaters and related models such as the Economaire, QuanTec, and Reno ranges — indicates that the boiler's control board has been unable to confirm adequate combustion airflow before the ignition sequence can proceed. In plain terms, the appliance expects to see a pressure differential of at least 0.48 mBar generated by the combustion air fan (CAF), which the air pressure switch (APS) must detect before the burner is allowed to light. If that signal never arrives — whether due to a sluggish fan, a blocked flue, a contaminated venturi, or a wiring issue — the boiler locks out and displays code 5. On Economaire and similar models, codes in the 4–9 range can also be triggered by a fault in the gas control valve assembly, including the electromagnetic coil or the combustion control board that sits directly on the valve, so a Gas Safe engineer will need to verify exactly which component is responsible.

Causes, fixes & costs for Johnson & Starley 5 → · All Johnson & Starley codes

Frequently asked questions

Is the 5 fault code the same on every boiler?

No. 5 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 5 fault myself?

Not usually. On every brand listed, 5 points to a fault that needs a suitably registered engineer to diagnose and repair. A single reset to rule out a transient glitch is reasonable; repeated resets are not.

Who should I call about a 5 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.