Nibe 220 Fault Code: Causes, Fixes & Repair Costs
What does the Nibe 220 fault code mean?
Alarm 220 on a NIBE system is a high pressure alarm: the outdoor heat pump unit has sent a fault message to the indoor controller reporting that refrigerant pressure on the high side of its circuit went out of range, and the compressor is blocked in response. High-side pressure climbs when the heat being produced cannot be shed — most often because water flow through the condenser is restricted (clogged filter, airlock, pump or diverter trouble), occasionally because of refrigerant-circuit faults or a pressure switch problem. It appears on split and VVM-based systems where an indoor module supervises an outdoor unit, and it is the NIBE counterpart of the high-pressure lockouts every refrigeration circuit carries.
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 through the condenser Common
A sludged filter, airlock, low pressure or a struggling pump slows the water carrying heat away; head pressure climbs until the switch trips — the most frequent real-world cause.
- Demand closed off during hot water or heating Sometimes
A sticking diverter valve or closed zones dead-head the circuit at the worst moment — classically during cylinder reheat, the hottest duty.
- Refrigerant circuit or pressure switch fault Sometimes
Overcharge, non-condensables, or a failing switch produce the same alarm — F-Gas engineer diagnosis once the water side is proven.
How to fix it
- Check system pressure and open heating zones DIY safe
Confirm heating system pressure is in the normal band and zones/radiators are open — give the heat somewhere to go before resetting.
- Acknowledge the alarm once and observe DIY safe
Reset/acknowledge the alarm on the indoor display a single time. If it returns, stop resetting — the outdoor unit is reporting a genuine condition and repetition only stresses the compressor.
- Have a suitably qualified heat pump engineer complete the documented checks heat pump engineer
The engineer will verify flow rate against commissioning, clean the filter, test the pump and diverter valve, and — with the water side proven — investigate the refrigerant pressures and the switch itself. 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
- High pressure switch · from £60
- 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 £100–£450, depending on the underlying cause.
Frequently asked questions
What does alarm 220 mean on my NIBE?
The outdoor unit reported refrigerant pressure too high on the discharge side and the compressor is blocked. It usually means the heat could not be carried away — restricted water flow is the prime suspect. Check pressure and open zones, reset once; recurrence needs an engineer's flow and refrigerant checks.
It trips mostly when heating hot water — why?
Cylinder reheat is the hardest duty: highest temperatures, and everything hanging on the diverter valve directing full flow to the coil. Marginal flow or a lazy diverter shows up there first. Tell the engineer the pattern — it points the diagnosis.
Is repeated resetting harmful?
Yes — each reset restarts the compressor into the same over-pressure conditions. One reset to clear a transient is fine; beyond that you are wearing the most expensive component in the system against a known fault.