6 Boiler Fault Code: What It Means on Every Brand

The 6 fault code appears on 3 brands — Halstead, Intergas and Nibe — 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 6 means	Severity	DIY?
HHalstead	Fault code 6 on Halstead boilers (including the Ace HE range) is a safety lockout triggered when the boiler's control board detects a flame signal for approximately 5 seconds after the… Full guide →	Lockout — engineer likely	No
IIntergas	Fault code 6 on an Intergas boiler indicates a flame detection problem. Full guide →	Lockout — engineer likely	No
NNibe	Fault Code 6 on a Nibe heat pump indicates a problem with the BT6 sensor — the primary temperature sensor responsible for monitoring and controlling domestic hot water (DHW) production. Full guide →	Engineer may be needed	No

6 brand by brand

Halstead 6

Fault code 6 on Halstead boilers (including the Ace HE range) is a safety lockout triggered when the boiler's control board detects a flame signal for approximately 5 seconds after the burner has been commanded to switch off. In other words, the boiler cannot confirm that the flame has been safely extinguished following a normal shutdown cycle. Because an uncontrolled or lingering flame presents a serious safety hazard, the boiler locks itself out entirely. This is not a fault you can simply reset your way past — the underlying cause must be diagnosed and resolved by a Gas Safe registered engineer before the boiler is used again.

Causes, fixes & costs for Halstead 6 → · All Halstead codes

Intergas 6

Fault code 6 on an Intergas boiler indicates a flame detection problem. The boiler's PCB (printed circuit board) is either expecting to see confirmation of a stable flame and not receiving it, or it is detecting a flame signal at a time when it shouldn't be. In practical terms, this usually means the burner is struggling to ignite and hold a flame, or the sensor responsible for confirming ignition is failing to report correctly. The boiler will typically lock out and refuse to operate until the underlying fault is resolved and the unit is reset.

Causes, fixes & costs for Intergas 6 → · All Intergas codes

Nibe 6

Fault Code 6 on a Nibe heat pump indicates a problem with the BT6 sensor — the primary temperature sensor responsible for monitoring and controlling domestic hot water (DHW) production. The system cannot obtain a valid temperature reading from this sensor, either because it has lost its electrical connection or because the sensor itself has failed. Without reliable DHW temperature data, the unit cannot regulate hot water output correctly. On VVM 500 units, the controller can fall back to the BT54 sensor and the alarm is configured for automatic reset, but on other models the fault may persist until the root cause is resolved.

Causes, fixes & costs for Nibe 6 → · All Nibe codes

Frequently asked questions

Is the 6 fault code the same on every boiler?

No. 6 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 6 fault myself?

Not usually. On every brand listed, 6 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 6 fault?

For gas boilers, a Gas Safe registered engineer — it is a legal requirement for any work on the appliance. For heat pumps, an MCS or F-Gas qualified heat pump engineer. 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.