30 Boiler Fault Code: What It Means on Every Brand

The 30 fault code appears on 3 brands — Intergas, Johnson & Starley and Viessmann — 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 30 means	Severity	DIY?
IIntergas	Fault code 30 on an Intergas boiler points to a problem with the gas valve relay. Full guide →	Lockout — engineer likely	No
JSJohnson & Starley	If your Johnson & Starley 30-series boiler (such as the WarmCair, Reno HE30C, QuanTec 30C, or RenoXtra 30C) has shut down and is showing a fault indication, it is important to know that… Full guide →	Engineer may be needed	No
VViessmann	Fault code 30 on Viessmann boilers signals that the burner control unit has entered a safety lockout because the fan has failed to come to a complete stop after a heating cycle, or because… Full guide →	Lockout — engineer likely	No

30 brand by brand

Intergas 30

Fault code 30 on an Intergas boiler points to a problem with the gas valve relay. The relay is a small electrical switching component within the gas valve assembly that the PCB uses to open and close the valve, controlling the flow of gas to the burner. When the boiler's control system detects that this relay is behaving unexpectedly — either not switching correctly or sending back an unexpected signal — it triggers a safety lockout and displays code 30. Because the fault is directly linked to the gas circuit, the boiler will not operate again until the underlying problem has been identified and resolved by a Gas Safe registered engineer.

Causes, fixes & costs for Intergas 30 → · All Intergas codes

Johnson & Starley 30

If your Johnson & Starley 30-series boiler (such as the WarmCair, Reno HE30C, QuanTec 30C, or RenoXtra 30C) has shut down and is showing a fault indication, it is important to know that Johnson & Starley warm air heaters do not use a straightforward two-digit numeric code system in the way many combi boilers do. Instead, the WarmCair range displays a small letter 'e' on screen when a fault has occurred. To reveal the actual fault code, press and hold the RESET button for more than one second, then release it — the specific fault code will then appear and can be cross-referenced with the chart in your boiler's manual or on the inside of the control board cover. If you are seeing '30' on your display, this may refer to your boiler model (e.g., Reno HE30C, QuanTec 30C) rather than a fault code. The most frequently reported shutdown causes on these 30-series appliances relate to fan faults, overheating due to blocked air filters or restricted airflow, condensate drainage blockages, and flame failure or ignition lockout issues. This page covers all of those fault categories so that whichever underlying problem triggered your boiler's shutdown, you can find practical guidance here.

Causes, fixes & costs for Johnson & Starley 30 → · All Johnson & Starley codes

Viessmann 30

Fault code 30 on Viessmann boilers signals that the burner control unit has entered a safety lockout because the fan has failed to come to a complete stop after a heating cycle, or because an unstable electrical connection to the fan has been detected. When the boiler finishes a cycle, the control unit expects the fan to idle down and halt within a defined window. If it keeps spinning — or if the fan speed signal received by the control board looks wrong — the boiler interprets this as a potential flue-gas hazard and locks out to protect the household. A secondary trigger for the same code is a loose or intermittent plug-in connection between the fan and the PCB, which can cause the controller to misread fan status entirely.

Causes, fixes & costs for Viessmann 30 → · All Viessmann codes

Frequently asked questions

Is the 30 fault code the same on every boiler?

No. 30 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 30 fault myself?

Not usually. On every brand listed, 30 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 30 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.