Nibe 45 Fault Code: Causes, Fixes & Repair Costs
What does the Nibe 45 fault code mean?
Nibe alarm code 45 indicates that the single-phase motor protection cut-out switch inside the heat pump has tripped, interrupting power to the compressor. This is a safety mechanism designed to prevent damage when abnormal current is detected. Until the underlying cause is identified and the fault is cleared, the unit will not provide heating or hot water.
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 motor protection breaker (MCB) Common
The most frequent trigger for this alarm. The internal motor protection cut-out switch has detected an overcurrent event and flipped to the off position. This can happen spontaneously during normal operation, during a power fluctuation, or even as a result of vibration during transportation or initial commissioning.
- Blocked or seized compressor Sometimes
A compressor that is struggling to start or has partially seized will draw far more current than normal, which trips the motor protection as intended. If the breaker trips again shortly after being reset, a failing compressor is a likely culprit.
- Wiring fault or loose connection Sometimes
Damaged, corroded or poorly terminated wiring between the terminal block and the compressor — or between the compressor and the soft-start card — can cause intermittent overcurrent conditions that repeatedly trip the motor protection breaker.
- Faulty soft-start card Rare
The soft-start card controls how the compressor ramps up to full speed. If this card develops a fault or has a blown fuse, it can prevent the compressor from starting cleanly, leading to excessive current draw and a tripped breaker.
How to fix it
- Switch off the heat pump at the main isolator and wait two minutes DIY safe
Cutting power fully before opening the unit is an essential safety precaution. Allow capacitors time to discharge before any panel is removed.
- Locate and reset the internal motor protection breaker heat pump engineer
The motor protection cut-out switch is housed inside the unit casing. Accessing it requires removing the front cover (two screws at the lower corners). Once located, toggle or press the breaker back to its 'on' position. Because this involves opening the unit and working near live electrical components, it should only be done by a qualified engineer — not a homeowner. Note: if your unit is still within its NIBE warranty period, opening the casing yourself may affect that warranty.
- Restore power and reset the alarm via the display DIY safe
Switch the isolator back on. On the controller display, select the alarm notification, choose 'I want to see more info about the alarm', then select 'Reset alarm and try again'. The unit will attempt to restart. Monitor whether heating resumes normally.
- If the alarm returns, do not keep resetting — call an MCS-certified engineer heat pump engineer
A breaker that trips again after reset points to an underlying fault: abnormal compressor current draw, a wiring issue, or a defective soft-start card. An engineer will use current-measurement tools to diagnose the compressor's condition, inspect all wiring and terminals, and test the soft-start card. Any work on the sealed refrigerant circuit requires an F-Gas registered engineer.
Parts you may need
- Motor protection cut-out breaker (MCB) · from £40
- Soft-start card (Nibe F1145 / F1245) · from £180
- Compressor wiring loom / terminal block · from £55
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
Can I reset Nibe fault code 45 myself?
You can safely attempt the display-level alarm reset (selecting 'Reset alarm and try again' on the controller). However, the physical motor protection breaker inside the unit requires removing the front casing, which should be done by a qualified engineer. If the alarm clears after the display reset and the unit runs normally, no further action may be needed. If it returns, stop resetting and call an engineer — repeated tripping indicates an underlying fault that won't fix itself.
How much does it cost to repair Nibe fault code 45 in the UK?
If a simple engineer visit, inspection and reset resolves the issue, expect to pay roughly £150–£250 including the callout. If the soft-start card needs replacing, total costs typically fall in the £300–£500 range. A compressor replacement — needed only in the worst-case scenario where the compressor has seized — is a much larger job costing upwards of £1,500–£2,500 depending on model and region. London and South East rates typically run 15–25% higher than the national average.
Why does this fault code mainly affect single-phase Nibe ground-source models?
Alarm code 45 specifically refers to the motor protection fitted on single-phase machines. Three-phase installations use a different protection arrangement. The F1145 and F1245 are the most common single-phase ground-source units in the UK market where this alarm appears, though you should always cross-reference your specific model's service manual to confirm the code meaning.
Is my Nibe heat pump still under warranty if I get fault code 45?
Standard Nibe warranty covers parts and labour for 24 months from installation (or 33 months from manufacture, whichever is shorter). Homeowners who used a Nibe Pro Partner or Pro Exclusive installer may have an extended 7-year parts and labour warranty. If you're within the warranty period, contact Nibe or your installing engineer before opening the unit yourself, as unauthorised disassembly could affect your cover. Nibe operates a UK network of Approved Repair Partners trained specifically on their products.