Nibe alarm 228 means the outdoor unit has failed to defrost ten times in a row, and alarm 83 on the F750 means a defrost did not finish within three hours. Either way, your heat pump is telling you that ice is not clearing as it should, which usually happens in a cold, damp spell.
The checks below are safe to try, but if the alarm comes back after one acknowledgement, book a Nibe heat pump repair rather than resetting it again. For every other Nibe alarm, see our full guide to Nibe heat pump error codes.
Please read first: this guide is here to help you understand what your Nibe heat pump is telling you. Every effort has been made to keep the information accurate, but manufacturers update their manuals and codes can differ between models and software versions, so always check the official Nibe manual for changes before acting on anything here. Do not attempt anything that could be dangerous, and avoid any work that could void your warranty. If in doubt, call a qualified heat pump engineer.
What does alarm 228 or 83 mean on a Nibe heat pump?
Alarm 228 means the heat pump has tried and failed to defrost its outdoor coil ten times in a row. It appears on SMO 40 systems, and Nibe links it to low heating flow, too little water in the system or a blocked particle filter.
Alarm 83 is the F750 version: a defrost started but did not meet its stop conditions within three hours. Nibe's alarm overview also groups alarms 158 and 159 with these as defrost faults, and points to the defrost function, the BT16 or BT76 sensor and the system volume.
Do not confuse either with alarm 183, which simply means a defrost is in progress. That one is normal and needs no action.
Is ice on a heat pump normal?
Yes, a light frost on the outdoor coil is normal in cold, damp weather, and the heat pump clears it with regular defrost cycles. During a defrost you may see steam, hear a whoosh and notice the fan stop for a few minutes, and the display may show alarm 183. Our guide to the heat pump defrost cycle explains what a normal one looks like.
It becomes a fault when the ice builds up and stays. A coil that is solid white, ice spreading over the casing or fan guard, or a block of ice growing under the unit all suggest defrosting is not working. That is when alarm 228 or 83 tends to appear, and our page on a frozen outside unit shows what to look for.
Why does alarm 228 or 83 appear in cold weather?
Defrost alarms show up in cold weather because that is when the coil collects the most frost and the defrost cycle has to work hardest. Nibe's documents list these causes:
- Low heating flow through the system
- Too little water in the system
- A blocked particle filter
- A fault in the defrost function or the BT16 or BT76 sensor
General engineering knowledge, not from the Nibe manuals, adds these underlying causes:
- Sludge or magnetite reducing flow, which a heat pump powerflush can clear
- A blocked strainer or an air lock in the pipework
- Low system pressure, covered in our guide to a heat pump losing pressure
- A frozen or blocked condensate drain, so meltwater refreezes under the unit
- Snow, leaves or stored items blocking airflow round the coil
- A unit sitting too low, so snow and ice pile up beneath it
- Low refrigerant, which only an F-Gas engineer can check
Our article on heat pumps in cold weather explains why output and efficiency drop in a cold snap.
What can you safely check yourself?
You can make a few outside checks safely, as long as you stay away from the inside of the unit.
- Keep the power on. Frost protection needs electricity, so do not switch off at the outdoor isolator unless an engineer tells you to.
- Clear snow, leaves and debris from around, above and under the outdoor unit, working from outside the casing.
- Check the condensate drain path is clear and not frozen. If it has iced up, thaw it with lukewarm water, never boiling.
- Look at the pressure gauge, if one is fitted, and check that radiator and isolation valves are open.
- If you are going away, use the holiday or frost settings rather than turning the system off. Our guide to heat pump holiday settings explains how.
- Acknowledge the alarm once on the display. Nibe says any alarm can be acknowledged safely, but it will come back if the cause is still there.
What not to do:
- Never chip, scrape or knock ice off the coil or fan.
- Never use boiling water, a heat gun or a hairdryer on the coil.
- Never remove panels or covers.
- Never touch the refrigerant pipework; only an F-Gas certified engineer can work on it.
Avoid switching the power off and on to clear the alarm, too. On the F2040, quick power cycling can itself trigger alarm 220.
When should you call an engineer?
Call an engineer if alarm 228 or 83 comes back after one acknowledgement, or if the outdoor unit stays encased in ice after you have cleared around it. Other clear signs:
- The house is getting cold or the hot water has stopped
- The pressure gauge keeps dropping
- Ice is forming on the pipework or casing, not just the coil
- A second alarm appears, such as 221 low pressure or 232 low evaporation temperature
- The fan grinds or will not turn
Several causes, including the defrost sensors and the refrigerant charge, sit inside the unit. Refrigerant work is legally restricted to F-Gas certified engineers, so a recurring defrost fault is not a DIY job. If the heat pump has stopped altogether, our guide to an air source heat pump not working covers other things to rule out.
How can you stop it happening again?
An annual service is the best way to stop defrost alarms returning, because it covers the filter, flow and airflow that Nibe links to alarm 228. Our annual service checklist shows what a good visit includes.
General engineering knowledge, not from the Nibe manuals:
- Have the magnetic or particle filter cleaned at every service.
- Make sure the system has the right inhibitor, plus antifreeze or freeze-protection valves where your installer designed it that way.
- Keep outdoor pipework well insulated.
- Stand the unit on raised feet with a clear path for condensate to drain away.
- Keep the clearances in your manual and site the unit away from drifting snow, falling leaves and roof run-off.
You will find more ideas in our heat pump winter tips.
Other Nibe codes you might see in a cold snap
These Nibe alarms often turn up alongside a defrost fault in freezing weather. Each links to our full Nibe code guide.
| Code | Meaning | What to do |
|---|---|---|
| 183 | Defrosting in progress | Normal; wait for it to finish |
| 180 | Anti-freeze active, outdoor below 3 °C | Information only |
| 158, 159 | Defrost stopped or failed (check your manual) | Engineer if it repeats |
| 221 | Low pressure, outdoor unit | F-Gas engineer |
| 232 | Low evaporation temperature (SMO 40) | F-Gas engineer |
| 224 | Fan alarm | Clear ice or debris from outside, then engineer |
| 271 | Outdoor air too cold to run | Wait for milder weather; engineer if it shows when mild |
Need help with a frozen Nibe heat pump?
If your Nibe is iced up and showing alarm 228 or 83, our emergency heat pump repair team can get to you quickly, with same-day visits where possible. Our F-Gas certified engineers check flow, filters, defrost sensors and the refrigerant circuit, then fix the cause rather than clearing the alarm.
We handle Nibe heat pump repairs across the UK, we are MCS accredited, and every repair comes with a 12-month guarantee. To stop defrost faults coming back, book annual heat pump servicing or join one of our heat pump cover plans. There is more about the brand on our Nibe heat pump page.
Call 0333 041 5130 or contact us online.
Frequently asked questions
Does cold weather cause alarm 228 on its own?
Cold, damp weather is what puts frost on the coil, but a healthy Nibe clears it with normal defrosts. Ten failed defrosts in a row means something is getting in the way, usually flow, system volume or the filter. The weather is the trigger, not the root cause.
Is it safe to leave an iced-up heat pump running overnight?
In most cases it is safer to leave the power on so frost protection can work, as long as there are no signs of damage. Clear what you can from outside and book an engineer for the morning. If you hear grinding or see ice on the fan blades, call us straight away.
Can repeated defrost failures damage the heat pump?
They can if left for long. Ice that keeps building can bend the fins, strain the fan and stop the unit producing useful heat. That is why we recommend getting a repeat alarm 228 checked rather than living with it.
Does acknowledging alarm 228 wipe it from the log?
No. Nibe logs its alarms, so an engineer can still see when 228 or 83 appeared after you have acknowledged it. Make a note of the date and the weather too, as that helps spot a pattern.
Will my heating still work while the alarm is showing?
The heat pump may struggle to deliver heat until the defrost problem is fixed. Depending on how your system was installed, back-up or extra heat may keep some warmth going, but it usually costs more to run. Do not rely on it for long.
