With cold snaps on the horizon, you might be wondering how to stop a heat pump freezing when temperatures drop significantly over the winter months.
A bit of snow and ice isn't usually anything to worry about, however, there are signs to look for if your heat pump does freeze and how you can rectify the situation quickly.
We go through the causes, the remedies and how to avoid causing damage to your heating system.
Heat pumps freezing: Causes and solutions
Homebuilding & Renovating's renewables expert David Hilton and expert on how heat pumps work, Peter Spurway from Viessmann take us through the essentials of how to stop a heat pump freezing.
How to stop a heat pump freezing
Unlike gas boilers vs heat pumps, which operate inside the home, heat pumps need to be equipped for changes in outdoor temperature. The good news is that all correctly installed heat pumps from reputable manufacturers shouldn't freeze in cold weather if they are functioning correctly.
Therefore you shouldn't normally need to do anything yourself to stop it from freezing.
David Hilton explains further: "All air source heat pumps that are designed to be installed outside of the home will have a defrost cycle. You'll know if this is taking place as during the defrost cycle there may be "a lot of ’steam’ that comes off the heat pump and possibly a 'whoosh' noise. Which is nothing to worry about as it is a normal feature of a heat pump."
However, whilst Peter Spurway at Viessmann explains that snow and ice resting on a heat pump aren't a problem, if you notice the whole unit is covered in ice as well as the insides of the coil, this could indicate a problem with your defrost cycle.
Whatever you do, don't go pouring water on the unit to defrost it as this is extremely dangerous. Attempting to remove the ice by chipping away at it can also cause serious damage to your heat pump.
Peter recommends you contact an HVAC professional who can help determine the cause. "When this problem is ignored, it can result in problems with your unit in the future, so it’s best to get it sorted sooner rather than later, so your heat pump can work in cold weather," says Peter.
David Hilton
With more than 35 years of expertise, David is a seasoned renewables and ventilation installer, recognised for his longstanding contributions to Homebuilding and Renovating magazine. With a Masters degree in Sustainable Architecture, David stands as an authoritative figure in sustainable building and energy efficiency. His extensive knowledge spans building fabrics, heat recovery ventilation, renewables (including heat pumps), as well as conventional heating systems.
Do not attempt to manually remove ice from your heatpump(Image credit: Viessmann Climate Solutions UK)
How to tell if a heat pump is frozen
"When a heat pump freezes there could be a number of symptoms," explains David Hilton.
If you're living with a heat pump, the first sign is that you will experience a noticeable drop in the output of your heat pump. "The ice that builds up on the evaporator (the finned area at the back of the heat pump) blocks the airflow and therefore affects the efficiency," says David.
He continues: "If the heat pump gets completely blocked with ice then it will be very visible on the back of the heat pump and also the output of the heat pump will drop and it will not be able to heat your water or home adequately. After a while, the heat pump may simply stop working and come up with a low-pressure fault."
Pete Spurway suggests in addition to the back of the unit being covered in ice, you might notice the unit periodically switching to defrost and plumes of warm water vapour being pushed outwards by the fan. All of these indicate that your heat pump is frozen.
(Image credit: Devgnor / Getty Images)
Peter Spurway
Peter is Head of Renewables at Viessmann Climate Solutions UK.
What causes a heat pump to freeze?
Low temperatures and high humidity can cause a heat pump to freeze in winter. "In cold weather, the condensed moisture on the coils of the heat pump freezes, forming ice. High humidity (we are an island nation after all!) increases the likelihood of frost formation," says Peter Spurway.
Part of good heat pump maintenance is to maintain airflow around your unit. "Consider the area around the unit, blocking a heat pump by parking too close or placing a bin or fence around to hide it could cause issues with airflow into the unit," says Peter.
If the heat sensor on your heat pump is faulty, it may not be able to detect the ice build-up, and this could be another reason the pump isn’t activating the defrost cycle, adds Viessmann.
(Image credit: Shutterstock)
FAQs
How does the defrost cycle on a heat pump work?
"The defrost function on an air source heat pump is an automatic feature that allows the heat pump to momentarily go into reverse to dump some heat on the evaporator," explains David Hilton, Homebuilding & Renovating's renewables expert.
"This is done to melt any ice build-up and thus open the fins to allow air to move freely. Inside the heat pump, there is a device called a 4-way valve that switches the flow of refrigerant to dump heat on the evaporator."
"There are a number of sensors in the heat pump unit that know when the evaporator is becoming blocked and will trigger the defrost cycle. Sometimes the defrost cycle can be tricked into operation when leaves block the evaporator or when dirt has blocked the condenser heat exchanger," finishes David.
What happens if a heat pump does not defrost?
"If the defrost cycle feature on your heat pump fails then the evaporator will build up with ice and airflow will be restricted as the fins get blocked up."
"Eventually, the heat pump will freeze up and completely block the airflow resulting in a lower output and potentially the heat pump could also stop working in order to protect itself," says renewables expert David Hilton.
How do you keep your home warm during a defrost cycle?
A heat pump myth is that a defrost cycle will cause your home to get colder. In fact, you shouldn't notice a temperature change inside your home during a defrost cycle, therefore there should be no need to prepare any backup heating.
"A defrost cycle will only operate for a few seconds to maybe a minute or two. It is not enough time to worry about it affecting the heat in the home," explains David Hilton.
"The defrost cycle reverses the unit operation, harnessing the indoor heat to melt the ice on the outdoor unit. This is why a suitable system volume is key; although if you notice reduced heating capacity it is advisable to contact your installer to look at the design and operation of the system in colder periods," says heat pump expert Peter Spurway.
There are many types of heat pumps available and choosing which type is right for you is a process. For instance check out our guide to solar assisted heat pumps and how they differ from the standard.
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Teresa was part of a team that launched Easy Gardens in 2018 and worked as the Editor on this magazine. She has extensive experience writing and editing content on gardens and landscaping on brands such as Homes & Gardens, Country Homes & Interiors and Living Etc magazine. She has developed close working relationships with top landscape architects and leading industry experts, and has been exposed to an array of rich content and expertise.
In 2020 Teresa bought her first home. She and her partner worked alongside architects and builders to transform the downstairs area of her two bedroom Victorian house in north London into a usable space for her family. Along the way she learned the stresses, woes and joys of home renovation, and is now looking to her next project, landscaping the back garden.
