Nibe 2 Fault Code: Causes, Fixes & Repair Costs
What does the Nibe 2 fault code mean?
Alarm code 2 on Nibe heat pumps indicates that the BT2 sensor — which monitors the temperature of water returning from the heating circuit back into the heat pump — is either disconnected or has failed. Without a valid reading from this sensor, the unit cannot safely manage heating output, so both the main heating function and any supplementary electric backup heating are blocked until the fault is resolved.
General guidance only — not a substitute for professional advice, and not certified by an heat pump engineer. Always have your specific appliance assessed by a qualified professional. Any heat pump work must be carried out by an MCS-certified heat pump engineer. If you notice a refrigerant leak, a burning smell or water leaking from the unit, switch it off at the isolator and call an MCS-certified heat pump engineer. Refrigerant work must be carried out by an F-Gas registered engineer.
Common causes
- Loose or disconnected sensor plug Common
The BT2 sensor connects to the control board via a plug and socket. Vibration over time, or disturbance during a recent service visit, can cause the connector to work loose, breaking the electrical circuit and triggering the alarm.
- Damaged sensor cable Common
The wiring running from the BT2 sensor to the control board can be nicked or severed — most often by rodent activity, accidental damage during maintenance, or wear where the cable passes through a tight aperture. Even a partial break in the cable can cause an intermittent or permanent open circuit.
- Failed NTC sensor element Sometimes
The BT2 is a standard NTC (negative temperature coefficient) thermistor. Like any electronic component it can fail over time, either going open circuit or short circuit. A healthy sensor reads approximately 10 kΩ at 25 °C; a significant deviation from the expected resistance curve confirms failure.
- Faulty control board input Rare
In less common cases, the terminal or input channel on the main PCB that accepts the BT2 signal can develop a fault, making the board unable to read a sensor that is otherwise intact. This is typically identified by an engineer after the sensor and wiring have been ruled out.
How to fix it
- Restart the heat pump from the controller DIY safe
Switch the unit off from the controller or the dedicated isolator, wait around 30 seconds, then power it back on. A transient electrical disturbance can occasionally trigger a sensor alarm that clears itself once the system reinitialises. If the alarm does not return, monitor the unit over the next few hours to confirm normal operation.
- Reset the alarm via the controller menu DIY safe
On Nibe controllers, an active alarm is indicated by a service-technician symbol in the display and a lit status indicator. Navigate to the alarm log in the menu and attempt a manual reset. If the underlying cause has been resolved — for example, a connector that reseated itself — the alarm will clear. If it returns immediately, the fault is still present.
- Check around the unit for obvious signs of cable damage DIY safe
Without opening the unit's casing, take a visual look at any sensor cables that are visible at the exterior of the indoor unit. Look for chewed insulation, kinks, or cables that appear to have been pulled taut. Do not attempt to open the casing, move any wiring, or test electrical continuity yourself — this is purely a visual check to give a useful report to your engineer.
- Contact an MCS-certified Nibe engineer to inspect and test the BT2 sensor heat pump engineer
An engineer will open the unit safely, locate the BT2 sensor at the heating return pipework, and check that the connector is fully seated at the control board. They will use a multimeter to measure the sensor's resistance against the expected NTC curve from the service manual. If the reading is outside tolerance, the sensor will be replaced. If the sensor tests fine, the engineer will trace the cable for breaks and, if necessary, test the relevant input channel on the PCB.
- Replace the BT2 sensor or repair the wiring as directed by the engineer's findings heat pump engineer
Sensor replacement involves disconnecting the old sensor from its pipe pocket and the control board, fitting a correctly specified NTC replacement, and verifying the reading in the service menu before returning the unit to normal operation. Where the cable is damaged, the engineer may repair or re-route it. PCB replacement is only required if the board input is confirmed faulty after all other causes are excluded.
Parts you may need
- BT2 NTC return temperature sensor · from £75
- Sensor cable harness (BT2 circuit) · from £45
- Nibe main control PCB (model-specific) · from £380
The exact spare depends on your boiler's GC number (on the data badge). Check this against the part before buying.
Typical repair cost
Expect to pay roughly £150–£350, depending on the underlying cause.
Frequently asked questions
Can my Nibe heat pump still provide hot water while alarm 2 is active?
It depends on your system setup, but in most cases alarm 2 blocks the heating function and supplementary heating while it is active. Hot water production via a separate DHW circuit may still operate if the relevant sensors are unaffected, but you should not rely on this. Check your controller display — if the hot water schedule is showing as blocked or the cylinder is not reaching temperature, treat it as a full system shutdown until the fault is cleared.
How long does it take to fix a BT2 sensor fault?
In most cases an engineer visit takes one to two hours. If the issue is simply a loose connector, the repair can be completed in the same visit once the engineer has the unit open. If a replacement sensor needs to be ordered, there may be a short wait — Nibe parts occasionally need to be shipped from stock, though many independent engineers carry common NTC sensors. Aim to get the fault attended to promptly, especially in cold weather, as backup heating is also blocked while alarm 2 is active.
Is alarm 2 on a Nibe heat pump an emergency?
It is not an immediate safety emergency in the way that a refrigerant leak or electrical fault would be, but it is a priority fault because it disables both your heating and any electric backup. In cold weather this can leave your home without heat relatively quickly. Contact an MCS-certified engineer promptly rather than leaving it for a routine appointment.
Could a faulty PCB cost more than the estimate shown?
Yes — if the sensor and wiring both test as healthy and the fault is traced to a failed input channel on the main control PCB, the board replacement cost can range from around £350 to over £600 for parts alone on some Nibe models, plus labour. However, PCB failure is the least common cause of alarm 2; the large majority of cases are resolved by a sensor or cable repair within the typical £150–£350 range shown above.