Nibe 6 Fault Code: Causes, Fixes & Repair Costs
What does the Nibe 6 fault code mean?
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.
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 wiring Common
The most frequent cause. The low-voltage cable connecting BT6 to the control board can work loose over time — particularly following any recent maintenance or servicing where the unit's panels were removed and refitted. Vibration from normal operation can gradually loosen terminals too.
- Corroded or damaged cable connections Sometimes
Moisture ingress, especially near the hot water cylinder or in the plant room, can cause oxidation at the connector terminals, increasing resistance or breaking the circuit entirely. Physical damage to the cable from being pinched or kinked during installation is another possibility.
- Failed BT6 thermistor Sometimes
Like any electronic component, the BT6 thermistor degrades over time. If the resistance characteristics of the sensor drift outside the acceptable range, the controller interprets this as a defective or absent sensor and raises the alarm.
- Control board fault Rare
In rare cases the sensor itself is fine but the input circuit on the main PCB that reads the BT6 signal has failed. This is typically only discovered after the sensor and its wiring have both been confirmed as good.
How to fix it
- Check whether the alarm has cleared itself automatically DIY safe
On many Nibe models, Fault Code 6 is configured for automatic reset. Wait a few minutes and observe the display — if the sensor reading stabilises for around 60 seconds the system may self-recover. If the alarm has cleared and hot water appears to be working normally, monitor the unit over the next day or so to confirm it does not recur.
- Attempt a manual reset from the controller DIY safe
If the alarm is still showing, navigate to the alarm notification on the Nibe display panel, select the option to view more information about the alarm, then choose 'Reset alarm and try again'. The display module will restart and the heat pump will attempt to resume normal operation. If the fault code reappears within a short time, the underlying cause has not been resolved and you should move on to the next steps.
- Check the isolator and consumer unit (MCB) DIY safe
Confirm the heat pump's dedicated MCB in your consumer unit has not tripped and that the local isolator on or near the unit is switched on. A brief loss of power can occasionally cause transient sensor faults. If an MCB has tripped and trips again on reset, stop and contact an engineer — do not repeatedly reset a tripping breaker.
- Inspect the sensor wiring connections — engineer task heat pump engineer
An MCS-certified Nibe engineer will open the unit and physically trace the BT6 sensor cable from the hot water cylinder sensor pocket to its terminal on the control board. They will check each connector for signs of looseness, corrosion, or mechanical damage, reseat any suspect connections, and re-test. The electrical wiring diagram specific to your model should be consulted during this process.
- Test the BT6 sensor resistance — engineer task heat pump engineer
Using a multimeter, the engineer will measure the resistance of the BT6 thermistor at a known temperature and compare the reading against the manufacturer's resistance-temperature table. A reading that is open-circuit, short-circuit, or significantly outside the expected range confirms a faulty sensor that must be replaced.
- Replace the BT6 sensor if confirmed defective — engineer task heat pump engineer
A qualified engineer will fit a compatible replacement BT6 sensor, ensuring the new unit is correctly seated in its pocket, the cable is routed and secured without strain or pinching, and all terminals are firmly connected. After replacement they will clear the fault, verify the controller is reading a plausible DHW temperature, and run a hot water cycle to confirm normal operation.
- Call an MCS-certified heat pump engineer if the fault persists or you cannot resolve it heat pump engineer
If the fault returns after sensor replacement, or if the sensor and wiring both test as good, the issue may lie with the main PCB's sensor input circuit. This requires further diagnosis by a qualified engineer. Use Nibe's own Approved Repair Partner network or an independent MCS-certified engineer experienced with Nibe systems. Note that any work involving the refrigerant circuit must be carried out by an F-Gas registered engineer.
Parts you may need
- Nibe BT6 hot water sensor (thermistor) · from £35
- Sensor cable loom / wiring harness · from £25
- Nibe main PCB (control board) · from £320
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 £160–£380, depending on the underlying cause.
Frequently asked questions
Can I keep using my Nibe heat pump for heating while Fault Code 6 is showing?
Possibly, yes. Fault Code 6 relates specifically to the hot water sensor, so space heating may continue to function depending on your system configuration and how your Nibe model handles the fault. However, domestic hot water production is likely to be unreliable or completely unavailable until the sensor issue is resolved. Check your display to see whether heating circuits are still active and monitor the unit closely.
How much does it typically cost to fix Nibe Fault Code 6 in the UK?
For most people, the total bill comes to roughly £160–£380 including call-out, labour, and the sensor part. Nibe's own fixed labour schedule lists a first-visit/diagnosis charge of around £90 and a sensor replacement labour charge of around £95, with the BT6 sensor part adding a further £30–£50 on top. If the fault turns out to be caused by the main PCB rather than the sensor itself, repair costs can rise significantly — PCB replacement typically runs to £400–£600 all in — but this is an uncommon outcome.
Will Fault Code 6 clear on its own without me doing anything?
On some Nibe models, including the VVM 500, Code 6 is set to automatic reset, meaning the controller will retry once it sees a stable sensor reading. If the cause was a temporary connection interruption it may clear itself. That said, if you are seeing the fault repeatedly or it will not clear, it is not safe to keep resetting it indefinitely — a recurring fault indicates a genuine sensor or wiring problem that needs a qualified engineer to investigate.
How long will I have to wait for a Nibe engineer and parts in the UK?
Nibe operates through a network of Approved Repair Partners across the UK and response times vary by region. Parts can sometimes involve a short lead time as Nibe's primary distribution is from Sweden, though many authorised partners and independent Nibe specialists hold common sensors in stock. If you are out of warranty and struggling to get a prompt response through official channels, an independent MCS-certified engineer who is familiar with Nibe systems and has access to parts suppliers can be a practical alternative.