1 Boiler Fault Code: What It Means on Every Brand

The 1 fault code appears on 4 brands — Halstead, Intergas, Johnson & Starley 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 4 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 1 means	Severity	DIY?
HHalstead	Fault code 1 on a Halstead boiler indicates that the appliance has detected an overheat condition — specifically, the water temperature inside the heat exchanger has climbed beyond 105°C. Full guide →	Lockout — engineer likely	No
IIntergas	Fault code 1 on an Intergas boiler signals that the boiler's water temperature has climbed beyond its safe operating limit — an overheat condition. Full guide →	Lockout — engineer likely	Some checks
JSJohnson & Starley	Fault Code 1 on Johnson & Starley boilers indicates that the boiler has attempted to light the burner and failed to detect a stable flame, resulting in a safety lockout. Full guide →	Lockout — engineer likely	No
NNibe	Nibe Alarm Code 1 indicates that the heat pump's outdoor temperature sensor, known as BT1, is either not connected or has been detected as defective. Full guide →	Engineer may be needed	Some checks

1 brand by brand

Halstead 1

Fault code 1 on a Halstead boiler indicates that the appliance has detected an overheat condition — specifically, the water temperature inside the heat exchanger has climbed beyond 105°C. When this threshold is breached, the boiler's safety thermostat trips and locks the unit out to prevent damage to internal components. The Safety Lockout LED will illuminate red. On certain Halstead models — notably the Ace HE range — fault code 1 can also be associated with ignition failure, where the burner attempts to light but fails and the boiler goes to ignition lockout. If you own an Ace HE, it is worth considering both scenarios: an overheat condition and an ignition lockout, as both can present as code 1 on your display. Always cross-reference with your specific model's installation manual if you have it to hand.

Causes, fixes & costs for Halstead 1 → · All Halstead codes

Intergas 1

Fault code 1 on an Intergas boiler signals that the boiler's water temperature has climbed beyond its safe operating limit — an overheat condition. When this happens, the boiler locks out and the red indicator flashes alongside the '1' on the temperature display. The root cause is almost always poor water circulation: if hot water cannot move freely around the system, heat builds up inside the boiler rather than being transferred to your radiators and hot water. Note that on some Intergas models the digit '1' during normal operation simply indicates the burner is firing — this is not a fault. A genuine fault code 1 is always accompanied by a flashing red indicator and a lockout, meaning the boiler stops producing heat until the underlying problem is resolved and the boiler is reset.

Causes, fixes & costs for Intergas 1 → · All Intergas codes

Johnson & Starley 1

Fault Code 1 on Johnson & Starley boilers indicates that the boiler has attempted to light the burner and failed to detect a stable flame, resulting in a safety lockout. On combi and heat-only models such as the Quantec HR28C, the display typically shows 'E1'. On warm air units like the Economaire, a single red LED character is visible through a small window in the front panel — Code 1 on that chart means the same thing: ignition has been attempted but no flame was established or detected. Once in lockout the boiler stops all heating and hot water until the fault is resolved and the unit is reset.

Causes, fixes & costs for Johnson & Starley 1 → · All Johnson & Starley codes

Nibe 1

Nibe Alarm Code 1 indicates that the heat pump's outdoor temperature sensor, known as BT1, is either not connected or has been detected as defective. The controller expects a continuous, valid reading from this sensor to calculate the correct flow temperature for your heating system. When the BT1 reading is absent or falls outside the expected range — typically due to an open circuit or short circuit on the sensor input — the unit raises Alarm 1 and falls back to a minimum calculated flow temperature. A red indicator light will appear on the top right of the indoor unit display alongside the alarm message.

Causes, fixes & costs for Nibe 1 → · All Nibe codes

Frequently asked questions

Is the 1 fault code the same on every boiler?

No. 1 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 1 fault myself?

On some brands there are safe homeowner checks first — typically system pressure, the condensate pipe in cold weather, and a single reset. Where the code is a simple pressure or reset condition, that may be all it needs. Never open the boiler casing yourself.

Who should I call about a 1 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.