Aira heat pumps do not publish a numeric low pressure code. Faults show as lights on the indoor unit and as “Errors” or “Critical errors” in the Aira Home Energy app, and the Aira material we reviewed does not say which of them means low water pressure. If the heating is weak, noisy or has stopped, read the pressure gauge, look for leaks, and book an engineer if the pressure keeps dropping.
If it keeps coming back, book an engineer rather than topping up or restarting repeatedly. You can book a heat pump repair online or call 0333 041 5130, and our full Aira heat pump error codes guide covers every other code.
Please read first: this article is a guide only. We make every effort to keep it accurate, but manufacturers update manuals and codes can differ between models and software versions, so always check the official Aira manual and support pages for your system. Do not attempt anything dangerous or anything that could void your warranty.
What does a low pressure fault mean on an Aira heat pump?
Low pressure means there is less water in the sealed heating circuit than there should be. The heat pump relies on that water to carry heat from the unit to your radiators or underfloor heating, so a drop can mean weak heating, noise, or the system stopping.
What Aira documents is limited. The Aira installation manual we read describes app alerts in two groups. “Errors” arrive as a push notification and the system keeps heating. “Critical errors” arrive as a text and push notification and mean the heat pump has stopped. Aira’s customer support page lists questions about a pulsating red light in the centre of the indoor unit, a pulsating red light on the left side, pulsating blue or solid green lights, and errors in the app. It does not, in the text we could read, say which of these relates to pressure.
We have not found an Aira document that gives a normal operating pressure for the water circuit in bar. The installation manual lists a heating system pressure of 2.5 bar in its product data, but does not explain whether that is a working or limit figure, so we are not quoting it as a target. Look at your own commissioning notes or ask your installer what your system should read cold. If you see a light or alert you do not recognise, Aira’s customer care team can confirm what it means for your unit.
Why does low water pressure happen on an Aira heat pump?
- A leak from a radiator valve, pipe joint, underfloor manifold, cylinder connection or the unit itself.
- An expansion vessel that has lost its charge, causing pressure swings as the water heats and cools.
- Air in the system. Air collects and reduces circulation, and bleeding it out drops the pressure.
- An automatic air vent that is leaking or has failed.
- Pressure relief valve discharge. The valve opens when pressure is too high and sends water to the drain.
- Radiator work or bleeding without topping up afterwards.
- Sensor faults that report low pressure when the system is actually fine, or the reverse.
- Frost or damage to outdoor pipework in a cold snap.
It helps to know how a loss of pressure tends to develop. A tiny weep at a joint might take weeks to show on the gauge, and the first thing you notice is a radiator that is slow to warm or a gurgle when the heating starts. A failed expansion vessel is different: the gauge climbs when the water is hot and drops when it cools, and the pressure relief valve may spit a little water each time. Air in the system tends to show up after work on the pipes. Knowing which pattern you have gives an engineer a head start, so write down what you see and when.
What can you safely check yourself?
- Find the pressure gauge in your installation and read it with the system cold. Write down the figure and the date.
- Look for drips, stains and damp around the indoor unit, cylinder, pipework and radiators. Check the pressure relief discharge pipe for wetness.
- Look at the lights on the indoor unit and the alerts in the app. Note colours, positions and whether they pulse. Take photos.
- Check that radiators, TRVs and any zone valves are open.
- Only top up through the filling loop if your Aira paperwork or installer has shown you how and you are competent. Stop at the figure your installer gave you. Our guide to a heat pump losing pressure explains why repeated drops matter.
- Check the gauge again in a day or two. If it has fallen, you have a leak or a fault.
What not to do:
- Do not do any refrigerant work. F-Gas certified engineers only.
- Never remove panels or covers from the indoor or outdoor unit.
- Do not keep over-pressurising the system.
- Do not ignore repeated top-ups.
- Do not leave a “Critical error” unanswered. The system has stopped.
If your Aira is new, remember that small amounts of air and a bit of settling are normal in the first weeks. Pressure that keeps falling after the first few top-ups is not normal, though, and should go back to whoever installed it or to an engineer for a proper leak test.
When should you call an engineer?
- The gauge drops again after you top up.
- You see a red light on the indoor unit or a “Critical error” in the app.
- Water is coming from the relief valve pipe.
- You can see damp, drips or a stain spreading.
- The heating or hot water has stopped.
- The system is noisy, gurgling or has cold radiators.
- You are unsure what the lights mean. Aira’s own care team is also worth contacting while your unit is under warranty.
Book early. If your Aira is under manufacturer or installer warranty, tell them about the fault before anyone works on it, so cover stays intact.
How can you stop it happening again?
- Have the system serviced every year. Our annual service checklist shows what a proper visit includes: pressure, expansion vessel, air vent, filters and a leak check.
- Look at the gauge every month and after any radiator bleeding.
- Deal with drips straight away. Our heat pump leaking water guide covers the usual causes.
- Check the heat pump commissioning checklist against your paperwork. It shows what pressure and flow records a new install should have.
- Keep app notifications switched on so you see alerts early.
- Leave valves where the installer set them.
Other Aira symptoms you might see with low pressure
Aira publishes lights and app alerts, not numeric codes, so this table lists symptoms. Confirm what any light means with Aira.
| What you see | What it may point to | First step |
|---|---|---|
| Pressure gauge reading falling | Leak, air vent, expansion vessel or relief valve | Check for drips; book an engineer if it falls again |
| Pulsating red light on the indoor unit | Listed on Aira’s support page as a fault light; meaning not confirmed here | Photograph it and contact Aira or an engineer |
| “Error” in the app | Per Aira’s manual, a push notification and the system keeps heating | Check the alert text and gauge; book a check |
| “Critical error” in the app | Per Aira’s manual, the heat pump has stopped | Check gauge and leaks, then call an engineer |
| Cold radiators, gurgling or knocking | Air or low pressure | Read the gauge; do not keep bleeding |
| Water at the relief valve pipe | Pressure relief valve has opened | Engineer to check the expansion vessel |
Need help with low pressure on an Aira heat pump?
UK Heat Pump Servicing engineers find the leak, check the expansion vessel and air vent and carry out heat pump repairs with a 12-month guarantee. We also offer an annual heat pump service and cover plans, so a falling gauge is picked up early. Contact us or call 0333 041 5130.
Frequently asked questions
Does Aira show the pressure in the app?
The Aira documents we reviewed do not say that the app displays system pressure, so we cannot confirm it. Read the gauge fitted to your installation and use the app for alerts.
Is a pulsating red light always a pressure problem?
No. It is listed as a fault indicator, but Aira’s support page does not say it means low pressure. Treat it as a fault that needs identifying, not a top-up prompt.
Can I use any water to top up?
Aira’s installation manual says the system must be filled with clean water, and that in the UK mains water is considered clean enough. Your installer will have used the correct method, so ask them before you add anything.
What is the difference between an Error and a Critical error?
According to Aira’s installation manual, an Error sends a push notification while the system keeps heating. A Critical error sends a text and push notification because the heat pump has stopped.
Do I need a heat pump engineer, or can a boiler engineer help?
Use someone with heat pump experience. Heat pump circuits, flow rates and refrigerant are different from a gas boiler, and anything involving refrigerant needs an F-Gas certified engineer.
