44 Boiler Fault Code: What It Means on Every Brand

The 44 fault code appears on 3 brands — Johnson & Starley, Nibe 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 44 means	Severity	DIY?
JSJohnson & Starley	Code 44 on a Johnson & Starley unit indicates a central-heating return sensor error — the return-side temperature probe has gone open or short circuit. Full guide →	Engineer may be needed	No
NNibe	Fault code 44 on a Nibe heat pump indicates that the soft start card has overheated or that its protective fuses have failed. Full guide →	Lockout — engineer likely	No
VViessmann	The F4 fault code — sometimes displayed as '44' on certain Viessmann boiler panels — means the boiler's control board did not receive a flame-confirmation signal from the ionisation sensor… Full guide →	Lockout — engineer likely	No

44 brand by brand

Johnson & Starley 44

Code 44 on a Johnson & Starley unit indicates a central-heating return sensor error — the return-side temperature probe has gone open or short circuit. On models that combine warm-air heating with a water circuit (WarmCair D/DW variants providing hot water, and Aquair heat interface units), the controller relies on the CH return probe to manage the water side safely; when its circuit fails in either direction, code 44 appears and normal operation is restricted. Diagnosis is the standard sensor routine: inspect the wiring and connectors, measure the sensor's resistance against the specification table, and replace the failed element.

Causes, fixes & costs for Johnson & Starley 44 → · All Johnson & Starley codes

Nibe 44

Fault code 44 on a Nibe heat pump indicates that the soft start card has overheated or that its protective fuses have failed. The soft start card is the electrical component responsible for managing the compressor's start-up sequence, gradually ramping up current rather than allowing a sudden surge. When this card or its fuses fail, the unit detects an unsafe condition and blocks the compressor from running, shutting down heating and hot water output until the fault is resolved.

Causes, fixes & costs for Nibe 44 → · All Nibe codes

Viessmann 44

The F4 fault code — sometimes displayed as '44' on certain Viessmann boiler panels — means the boiler's control board did not receive a flame-confirmation signal from the ionisation sensor within the expected ignition window. In plain terms: the burner tried to light, but the electronics could not verify that a stable flame was present, so the boiler shut itself down as a safety precaution. Until the underlying cause is resolved, you will have no central heating or hot water. One specific sub-code worth noting is F4 EE (or 44 EE), which indicates a frozen condensate pipe rather than an ignition component fault — this is the one scenario a homeowner can safely address themselves by thawing the pipe with warm water.

Causes, fixes & costs for Viessmann 44 → · All Viessmann codes

Frequently asked questions

Is the 44 fault code the same on every boiler?

No. 44 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 44 fault myself?

Not usually. On every brand listed, 44 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 44 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.