Nibe 41 Fault Code: Causes, Fixes & Repair Costs
What does the Nibe 41 fault code mean?
Fault code 41 indicates that phase 2 of the three-phase electrical supply to the compressor has either dropped completely or remained below 160V for more than 30 consecutive minutes. When this threshold is breached, the heat pump's control system blocks the compressor as a protective measure, bringing heating and hot water to a halt until the underlying electrical issue is resolved and the alarm is manually cleared in the controller menu. This code only appears on three-phase NIBE models (typically larger ground-source units and some bigger air-source installations running on a 3×400V supply).
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
- Tripped MCB or blown fuse on phase 2 Common
A tripped miniature circuit breaker or blown fuse on the phase 2 circuit is the most straightforward trigger. Check the consumer unit or dedicated heat pump isolator panel for any tripped breakers — this is the one check a homeowner can carry out safely before calling an engineer.
- Loose or damaged wiring connection Common
A loose terminal, corroded connection or damaged cable on the phase 2 supply can cause an intermittent or sustained voltage drop below the 160V threshold. This type of fault may not trip a breaker and requires an engineer to inspect the wiring from the supply board through to the heat pump terminals.
- Faulty softstart card or capacitor Sometimes
The softstart card manages how the compressor ramps up to speed and protects it from electrical stress. If the softstart card or associated capacitor degrades, it can cause phase imbalances or apparent phase loss. Real-world NIBE service cases have confirmed this component combination as a cause of phase-fault alarms, requiring replacement of both parts.
- Sustained low grid voltage on phase 2 Sometimes
In some rural or older properties, the incoming three-phase supply may be consistently low on one phase, particularly under heavy-load conditions. If phase 2 from the grid regularly sags below 160V, the alarm will trigger without any fault in the heat pump itself. A qualified electrician or the Distribution Network Operator (DNO) would need to investigate.
- Worn or struggling compressor Rare
On older units, a compressor nearing end of life may draw uneven current across the three phases. The resulting imbalance can cause phase 2 to appear absent to the control board even when the supply is technically present. If all electrical components check out, the compressor itself may need assessment.
How to fix it
- Check for a tripped MCB at the consumer unit or heat pump isolator DIY safe
Locate your property's consumer unit and any dedicated isolator panel for the heat pump. Look for a tripped breaker — one that has flipped to the middle or off position — and reset it once. If it trips again immediately, do not reset it further and call an engineer; a recurring trip indicates a genuine fault.
- Inspect the area around the outdoor unit and ensure the unit has power DIY safe
Confirm the outdoor unit isolator switch is in the on position and that there are no obvious signs of physical damage to the unit or supply cable. Do not open any electrical enclosures.
- Do not attempt to work on the three-phase supply wiring yourself heat pump engineer
Three-phase electrical work is notifiable and potentially lethal. Only a Part P-registered electrician or a qualified heat pump engineer may safely inspect, test and repair the incoming phase supply, wiring and terminals. Do not attempt to swap, reconnect or bypass any phase conductors.
- Have an engineer verify that all three phases are present and within voltage tolerance heat pump engineer
An MCS-certified heat pump engineer or electrician will use a multimeter or phase tester to confirm that phases 1, 2 and 3 are all delivering a voltage within acceptable limits at the heat pump terminals. If phase 2 is genuinely absent or low, the supply route back to the distribution board will be traced and any fault rectified.
- Have the softstart card, capacitor and wiring connections inspected and replaced if faulty heat pump engineer
If the incoming supply is confirmed healthy, the engineer will inspect the softstart card and associated capacitor. These are internal electrical components that require a NIBE-trained engineer to test and replace correctly. Incorrect handling risks further damage to the compressor.
- Have the compressor assessed if electrical components are in good order heat pump engineer
Should the supply, wiring and softstart all test satisfactory, the compressor itself may be drawing uneven current. A heat pump engineer can assess compressor health using electrical measurements. Compressor replacement is a major job that must be carried out by an MCS-certified engineer; any refrigerant handling requires an F-Gas registered engineer.
- Manually reset the fault in the NIBE controller menu once the root cause is resolved DIY safe
Fault code 41 does not clear automatically. Once the engineer has confirmed the underlying electrical issue is fixed, navigate to the alarm or fault log in the NIBE controller and confirm the reset. The compressor will remain blocked until this step is completed. Do not reset repeatedly without resolving the cause first, as this can mask a dangerous fault.
- Contact a NIBE-approved engineer or MCS-certified heat pump specialist if the fault persists or recurs heat pump engineer
If the fault returns after clearing, or if you are unsure about any step, contact NIBE's UK homeowner support line or book an MCS-certified heat pump engineer. Any work involving the refrigerant circuit or compressor internals must be carried out by an F-Gas registered engineer.
Parts you may need
- Softstart card (NIBE compatible) · from £180
- Softstart capacitor · from £35
- Phase monitoring relay · from £45
- Miniature circuit breaker (3-phase, appropriate rating) · from £25
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–£500, depending on the underlying cause.
Frequently asked questions
Why does NIBE fault code 41 only appear on some models?
Fault code 41 is specific to NIBE heat pumps that operate on a three-phase 400V electrical supply. Smaller single-phase units simply do not have a phase 2 or phase 3 to monitor, so they cannot generate phase-loss alarms. If your property has a single-phase supply, this code will not appear on your system.
Can I just keep resetting fault code 41 to get my heating back on?
We strongly advise against this. The control board blocks the compressor specifically to prevent it from running with a degraded or absent phase, which could cause serious electrical damage or complete compressor failure. Repeatedly forcing resets without fixing the root cause risks a much larger repair bill — potentially a full compressor replacement costing around £2,000 or more.
How long will the repair take and will I be without heating?
A straightforward fix such as a tripped breaker or a loose terminal can be resolved in a single engineer visit, typically restoring heating the same day. A softstart card replacement usually takes a few hours once the part is available. Compressor replacement is a more significant job and may take a day or require ordering parts, leaving you without heating for longer — it is worth asking your engineer about a temporary electric backup heater in cold weather.
Do I need an F-Gas engineer for fault code 41?
Not necessarily. Fault code 41 is an electrical fault and most repairs — checking the supply, replacing wiring, swapping the softstart card — do not involve the sealed refrigerant circuit. However, if the investigation reveals a failing compressor that requires replacement, that work will involve the refrigerant circuit and must be carried out by an engineer who holds an F-Gas qualification, in addition to their MCS certification.