11 Boiler Fault Code: What It Means on Every Brand

The 11 fault code appears on 2 brands — 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 2 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 11 means	Severity	DIY?
IIntergas	Fault code 11 on an Intergas boiler indicates that the boiler's control board has detected either a problem with the S1 temperature sensor or a circulation fault. Full guide →	Lockout — engineer likely	No
NNibe	Fault code 11 on Nibe heat pumps indicates a problem with the BT11 sensor — the temperature probe fitted to the pipework at the condenser (heat exchanger) outlet inside the unit. Full guide →	Engineer may be needed	No

11 brand by brand

Intergas 11

Fault code 11 on an Intergas boiler indicates that the boiler's control board has detected either a problem with the S1 temperature sensor or a circulation fault. The S1 sensor sits on the heat exchanger and monitors the flow water temperature. When you call for heat, the PCB expects to see the flow temperature rise within a set time. If the S1 sensor isn't reporting the expected temperature increase — whether because the sensor itself is faulty or because water isn't circulating properly around the heat exchanger — the boiler locks out to protect itself from damage. Note that fault codes 10 through 14 all relate to heat exchanger sensor issues, with codes differing by which sensor or condition has triggered the lockout.

Causes, fixes & costs for Intergas 11 → · All Intergas codes

Nibe 11

Fault code 11 on Nibe heat pumps indicates a problem with the BT11 sensor — the temperature probe fitted to the pipework at the condenser (heat exchanger) outlet inside the unit. The control system uses this sensor to monitor the water temperature leaving the heat exchanger and regulate heating output accordingly. When the BT11 reading is absent or implausible, the system cannot manage flow temperatures correctly, so it defaults to a minimum calculated flow temperature and heating performance is significantly reduced or blocked entirely until the sensor issue is resolved. A red indicator light will appear on the unit and the alarm number will be shown on the display.

Causes, fixes & costs for Nibe 11 → · All Nibe codes

Frequently asked questions

Is the 11 fault code the same on every boiler?

No. 11 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 11 fault myself?

Not usually. On every brand listed, 11 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 11 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.