Nibe 50 Fault Code: Causes, Fixes & Repair Costs
What does the Nibe 50 fault code mean?
Fault code 50 on a Nibe heat pump indicates that the high-pressure switch has been activated more than once in quick succession. When this happens, the unit locks out the compressor and requires a manual reset before it will run again. In plain terms, the refrigerant pressure on the high side of the system has climbed beyond a safe threshold — and because it happened repeatedly rather than as a one-off blip, the heat pump refuses to restart automatically as a protective measure. In the vast majority of cases, the root cause is not the refrigerant circuit itself but poor water flow through the heating-side heat exchanger, which prevents the heat pump from shedding heat efficiently and causes pressure to rise.
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
- Low system water pressure Common
Nibe heat pumps typically need at least 1 bar of static pressure in the heating circuit to maintain adequate water flow. If the system has lost pressure — often through a small leak or a recently bled radiator — flow through the plate heat exchanger drops and refrigerant pressure climbs. Check the pressure gauge on the unit or the filling loop manifold; it should normally read around 1.0–1.5 bar when the system is cold.
- Blocked particle filter or strainer Common
Most Nibe installations include a strainer or particle filter in the heating circuit pipework. Over time this can collect debris, scale or magnetite sludge, restricting flow enough to trigger a high-pressure lockout. A partially blocked filter is one of the first things an engineer will check and is often the culprit on older installations.
- Air lock in the heating circuit Common
Air trapped in the pipework or within the heat pump's internal water circuit reduces effective flow rate. This is particularly common after the system has been drained, refilled or had work carried out on it. Symptoms include gurgling noises and uneven heat distribution alongside the fault code.
- Closed isolation valve or zone valve Sometimes
If an isolation valve near the heat pump, the cylinder coil or a zone valve has been partially or fully closed — perhaps after maintenance — flow is restricted on one or more circuits. A closed cylinder zone valve during a domestic hot water call is a surprisingly frequent cause of fault 50.
- Circulation pump failure or reduced output Sometimes
If the heating medium pump (the pump circulating water around the heat pump's internal circuit) has failed, seized, or is running at a reduced speed due to a fault, water cannot flow freely through the heat exchanger. This is less common than flow-restriction issues but requires an engineer to diagnose and rectify.
- Faulty high-pressure switch or wiring Rare
In rare cases the pressure switch itself or its wiring connection is the problem rather than actual high pressure in the system. A loose connector or a switch that has drifted out of calibration can produce spurious lockouts even when water flow is perfectly adequate.
How to fix it
- Check the system water pressure gauge DIY safe
Locate the pressure gauge — usually on the Nibe indoor unit or nearby pipework. If it reads below 1.0 bar, the system needs topping up via the filling loop. Slowly open the filling loop valve until the gauge reads around 1.0–1.5 bar, then close it again. Refer to your installer's commissioning sheet for the exact target pressure.
- Bleed radiators and any manual air vents DIY safe
Work through each radiator using a bleed key, starting on the ground floor and working upwards. Also check any automatic air vents on the system, particularly any located on the heat pump's pipework manifold. After bleeding, recheck system pressure and top up again if it has dropped below 1.0 bar.
- Check that all isolation valves are fully open DIY safe
Trace the pipework around the heat pump, the buffer vessel (if fitted) and the hot water cylinder. Ensure every isolation valve is in the open position — the handle should be in line with the pipe. Pay particular attention to the coil isolation valves on the cylinder.
- Check for debris around the outdoor unit DIY safe
Although fault 50 is primarily a water-side issue, ensure the outdoor unit's air intake and discharge are clear of leaves, snow, ice or other obstructions. Restricted airflow can contribute to high-side pressure problems in some conditions.
- Attempt a manual reset from the controller DIY safe
Once you have completed the checks above, navigate to the alarm menu on the Nibe controller (typically via Menu → Alarm Log on SMO or HMI displays). Select the active fault 50 alarm and confirm the reset. The compressor should attempt to restart. If the alarm returns within a short time, do not keep resetting — move to the next step.
- Check and clean the particle filter or strainer heat pump engineer
The strainer is located in the heating circuit pipework, but isolating, draining and cleaning it involves working on the pressurised water system and reassembling correctly to avoid leaks. Unless you are confident and competent with plumbing work, this is best left to an engineer. Do not attempt to access any refrigerant-side components.
- Call an MCS-certified Nibe engineer heat pump engineer
If the alarm persists after the homeowner checks above, or if the system pressure keeps dropping, arrange a visit from an MCS-certified heat pump engineer — ideally a Nibe Approved Repair Partner. They can pressure-test the water circuit, inspect the circulation pump and zone valves, check the pressure switch and wiring, and assess the refrigerant circuit. Any work on the refrigerant (sealed) circuit must only be carried out by an F-Gas registered engineer. You can also contact Nibe's homeowner care line on 0330 311 2201 (option 1) for guidance before booking.
Parts you may need
- Heating circuit strainer / particle filter · from £25
- Circulation pump (heating medium pump) · from £180
- Zone valve (cylinder or heating circuit) · from £65
- High-pressure switch · from £45
- System inhibitor and filter cleaner (e.g. Fernox F1) · 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 £120–£550, depending on the underlying cause.
Frequently asked questions
Can I reset a Nibe fault code 50 myself?
Yes — you can attempt a manual reset from the Nibe controller after carrying out the basic checks (system pressure, bleeding air, confirming all valves are open). If the alarm clears and does not return, you may not need an engineer at all. However, if the lockout comes back within a day or two, stop resetting and call an engineer. Repeated resets without fixing the underlying cause can stress the compressor.
Why does fault 50 keep coming back on my Nibe heat pump?
A recurring high-pressure alarm almost always means the root cause has not been resolved. The most common culprits are a partially blocked strainer that needs cleaning, a slow system pressure leak that keeps dropping below 1 bar, or a circulation pump that is losing performance. An engineer will carry out flow-rate and pressure-drop testing to pinpoint which part of the water circuit is at fault.
Will fixing fault 50 affect my Nibe warranty?
Homeowner checks such as topping up system pressure and bleeding radiators will not invalidate your warranty. However, repairs carried out by engineers who are not Nibe Approved Repair Partners could affect warranty terms — check your documentation. Keeping the heat pump serviced annually is also typically a warranty condition, so make sure you have a service record in place.
Could fault 50 ever be caused by a refrigerant problem rather than a water-flow issue?
In the majority of cases, fault 50 is a water-side flow problem and not a refrigerant circuit fault. However, if the refrigerant charge is incorrect (overcharged or contaminated), high-side pressure can rise independently of water flow. An F-Gas registered engineer can connect refrigerant gauges to check the system pressures and refrigerant charge. This is not something a homeowner or non-F-Gas engineer should attempt. In the rare event that a compressor fault is causing the issue, replacement costs can reach around £1,500–£2,000, though this is well outside the typical repair scenario for fault 50.