Why is my heat pump blowing cold air? Experts warn it could be one of these five things — and three of them need immediate attention

A heat pump is a hefty investment, so you'll want it to run as smoothly as possible. And while there’s no doubt that this efficient heating system will pay off in the long run - both financially and environmentally - there may unfortunately come a time when you wonder: Why is my heat pump blowing cold air?

Installing a heat pump is one of the best ways to save energy at home, and air-source heat pumps often consist of an exterior and internal unit that can either blow warm or cold air into your property. But when winter comes along, and you want it to heat your home, you may start to question whether a heat pump is worth it when it stops working as it should.

If your heat pump is blowing cold air, you’ll be happy to know we’ve spoken to experts familiar with such a phenomenon. And while there might not be any need for concern, they’ve revealed the five potential reasons why it’s happening - and what you can do about it.

1. There might not be anything wrong with it

If you’ve recently had a heat pump installed and are new to this type of heating system, questioning why your heat pump is blowing cold air could leave you wondering whether you’ve made a poor investment. But according to experts, there might not be anything wrong with it.

Michael Zohouri, founder of The Retrofitters, says, ‘When a heat pump blows cool air in heating mode, it doesn’t always mean something is wrong. Heat pumps typically produce air between 29–32°C, which can feel cool compared to body temperature but still effectively warms the home.’

He adds, ‘Unlike gas boilers or furnaces that provide bursts of high heat, heat pumps deliver consistent, lower-level warmth. This can sometimes confuse homeowners who are new to using heat pumps - they assume something must be broken or not set up correctly.’

Yes, it might just take you a little while to get used to a heat pump. But he does say that if you put your hand up to the internal unit and believe the air coming out is indeed colder than it should be, then you’ll need to look a bit closer to determine whether there's a bigger problem at hand.

2. It’s in defrost mode

Your heat pump could also be blowing cold air temporarily - especially if you’ve noticed it during the harsh winter months and your heat pump is not hidden from the elements. This is because heat pumps often enter into a ‘defrost mode’ when temperatures drop to extreme levels.

Michael says, ‘When the outdoor unit starts to ice up in colder weather, the heat pump automatically switches to defrost mode to melt that ice. During this time, the system might blow cooler air indoors for a few minutes. It’s completely normal and should switch back to heating once the ice has cleared.’

Of course, if your heat pump doesn’t resume scheduled programming within a few minutes, you should once again inspect it further.

3. There’s a refrigerant leak

One thing most people don’t know is that heat pumps cannot work without refrigerant. This refrigerant is the same as those used in refrigerators, and the compressed gas is used to move heat around the system to heat your home effectively.

So, your heat pump may be blowing cold air because of a refrigerant leak. ‘If the refrigerant level is low, often due to a leak, the system can’t move heat effectively, so the air blowing out will feel cooler than it should,’ says Michael. ‘This definitely needs professional attention because a refrigerant leak can worsen over time and reduce the system's efficiency.’

This is echoed by David Leviseur, CEO and co-founder of heat pump specialist Fornax, who advises, ‘As a first step, you should contact the engineer who installed the system originally; it may be under workmanship or equipment warranty, and they can diagnose and repair at no cost or, if it's out of warranty, quote for doing so.’

4. There’s a problem with the reversing valve

Although the refrigerant is an essential component of a heat pump, it would be nothing without the reversing valve. This valve allows the heat pump to change the direction of refrigerant flow - which allows you to change between heating and cooling modes.

‘If it’s faulty or stuck, the system might be stuck in cooling mode, even when you’ve set it to heat,’ explains Michael. So, that might be the reason why your heat pump is blowing cold air.

However, it’s important to note that you shouldn’t attempt to fix this yourself as you may make the problem worse. In this instance, contact your heat pump engineer and book in for a specialist technician to fix it.

5. The filters are clogged

No matter whether you have one of the best vacuum cleaners, air purifiers, or heat pumps, you need to keep on top of filter cleaning. In fact, one of the biggest reasons why a heat pump blows cold air is because the filters are clogged and dirty.

Michael explains, ‘If the filters are clogged, airflow gets restricted, and that makes it much harder for the heat pump to circulate warm air effectively. Replacing or cleaning filters regularly can make a big difference.’

And while you can potentially do this yourself (by following the guidance in your instruction manual), most experts would suggest either waiting for your heat pump service or calling in a professional to do it for you.

As Rob Jennison, Service & Maintenance Manager at Geo Green Power, says, ‘As with all heating systems, an annual service to check everything is in good working order, clean filters and carry out routine maintenance is important in making sure that your heat pump is ready for winter.’

FAQs

Why is my heat pump blowing lukewarm air?

If your heat pump is blowing out lukewarm air that’s neither hot nor cold, it could be due to one of the following reasons:

• It’s running low on refrigerant.
• The thermostat has been turned down.
• The filter needs cleaning.

What is the best temperature for a heat pump in the winter?

While this ultimately depends on your own personal preference, most experts would advise keeping your heat pump at around 18-22°C in winter. This will keep your home comfortable and warm without stretching the heat pump (and, therefore, your energy bills) too far during the colder months.

However, if you find that this is too cold, you can turn it up an extra degree or so.

If your heat pump has been blowing cold air, hopefully, now you’ll understand the reason why and will be able to get it sorted in no time.