Nibe 150 Fault Code: Causes, Fixes & Repair Costs
What does the Nibe 150 fault code mean?
Alarm 150 on a NIBE heat pump means high condenser out temperature: the water leaving the condenser — the heat exchanger where refrigerant hands its heat to your heating water — has reached the maximum the unit permits, and it has stopped to protect itself. A condenser running away hot almost always means the heat being produced is not being carried off: too little water flow (clogged filter, airlock, pump trouble), too little demand (valves closed, zones shut, an undersized buffer), or control settings pushing temperatures the hydronics cannot absorb. It sits alongside NIBE's alarm 155 (hot gas over 135°C) as the water-side face of the same physics: heat with nowhere to go.
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
- Restricted water flow Common
A sludged filter, an airlock, low system pressure or a struggling pump slows the water that should carry heat away — condenser temperature then climbs to the limit.
- Demand suddenly closed off Common
Zone valves shutting, TRVs all closed, or a diverting valve sticking leaves the heat pump pushing heat into a dead-headed circuit.
- Settings or charge-side issues Sometimes
Curves or hot water targets set beyond what the emitters can shed, or refrigerant-side faults, produce the same climb — engineer diagnosis.
How to fix it
- Check system pressure and that heat can flow somewhere DIY safe
Confirm pressure is in the normal band (top up if below ~1 bar per your manual) and that radiators/underfloor zones are actually open — a system with every valve shut gives the heat pump nowhere to put its output.
- Acknowledge the alarm once and observe DIY safe
On the display, select the alarm and choose to reset/acknowledge it (or use 'aux. operation' if offered, which keeps some heating running). One reset is legitimate; if the alarm returns, leave it for an engineer rather than resetting repeatedly.
- Have a suitably qualified heat pump engineer complete the documented checks heat pump engineer
The engineer will clean the filter, bleed and verify the flow rate against commissioning, test the circulation pump and any diverter valve, and review temperature settings — investigating the refrigerant side only if the water side is proven. Any work on the sealed refrigerant circuit legally requires an F-Gas registered engineer; a NIBE-accredited (NIBE Pro) installer is the natural choice.
Parts you may need
- Circulating pump · from £150
- Magnetic filter clean/service · from £20
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 £90–£400, depending on the underlying cause.
Frequently asked questions
What does alarm 150 mean on my NIBE?
Water leaving the heat pump's condenser hit the maximum permitted temperature, so the unit stopped — its heat was not being carried away fast enough. Check the system pressure and that heating zones are open, reset once, and if it returns have the flow rate, pump and filter checked.
It happens mainly during hot water heating — why?
Cylinder reheating runs the highest temperatures the system ever sees, so marginal flow shows up there first. A part-blocked filter or a lazy diverter valve often passes in heating mode and fails on hot water — tell the engineer the pattern, it narrows things quickly.
Could my settings cause this?
Yes — hot water or curve targets set optimistically high can push the condenser to its ceiling, especially on systems with small radiators. Part of the fix can simply be settings that respect what your emitters can shed.