Hot Tub Heat Pump Winter Care: Frost, Draining and Servicing
Leave it on, and it looks after itself in the cold.
A hot tub heat pump that stays powered, with the water circulating, protects itself from frost: below 2°C it warms the water back up on its own. If you switch it off for winter, drain it once the air drops below 3°C. Clean it gently and have it serviced once a year.1
Leaving it on through winter
Frost protection, built in
When the heat pump has been on standby for over two hours and the air or water falls below 2°C, it starts its compressor and the circulating pump to warm the water back above 2°C. It stops once the air is back above 2°C or you switch it on. For this to work, it must stay powered with the hot tub's pump running.1
Keep the grilles clear of snow and leaves, with 1 metre clear in front of the fan and 50 cm at the sides and back. Never cover a heat pump that is running.1 Our guide on connecting a heat pump to a hot tub shows the bypass valves mentioned below.
The temperatures to know
Read down from warm to cold. These are the points where your heat pump does something different.
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40°C
The warmest it heats the water to
Our heat pumps heat water from 15°C to 40°C.1
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3°C
Winterise a heat pump you have switched off
Below 3°C, drain a heat pump that is shut down for the season.1
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2°C
Frost protection starts
On standby, it heats the water if the air or water drops below 2°C.1
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-7°C
The coldest air our 7kW works in
Still giving about 3 kWh of heat for each kWh of electricity.1
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-14°C
The coldest air our 12kW works in
With a base plate heater to stop ice building up.2
Switching off for winter: four steps
If you are not using the hot tub over winter and want the heat pump switched off, drain it before the air drops below 3°C, so no water freezes inside it.1
Switch off and isolate
Switch off at the control panel, then disconnect the heat pump from the power at its isolator.
Turn the water around it
Open the bypass valve fully, then close the valves on the heat pump's inlet and outlet. The hot tub keeps circulating without it.
Drain the heat pump
Unscrew the water pipe connections on the heat pump so the water inside drains out.
Close up and cover
Screw the connections back on, or block the openings with clean rags, so nothing gets into the pipes. Then fit its winter storage cover.
If the hot tub's circulating pump is controlled by the heat pump, drain that as well.1 To start again in spring, reverse the steps and set the bypass valve back to half open.
Cleaning and the yearly service
What you can do
Switch off and isolate the power first. Wipe the casing with a damp cloth, without detergents, which can damage the finish. Clean the evaporator fins at the back gently with a vacuum cleaner and a soft brush attachment. Keep the hot tub's filter clean too, as the heat pump sits after it.1
Once a year, a qualified person
Book a yearly check of the safety devices, the electrical wiring and the earthing, and the refrigerant pressure gauge. After a long time switched off, the gauge should read at least 80 PSI before you start it.1
If it won't start
Run through these five checks first.1
- Has it been standing upright for at least 2 hours?
- Is it switched on and connected to the power?
- Is the fuse OK?
- Switch it off, wait 3 minutes and switch it on again.
- Is the hot tub full, with water flowing to the heat pump?
Still not running? Contact our team or call 01482 212322, 9am to 5pm, Monday to Friday.1 You can see all our air source heat pumps, or read is a heat pump worth it for a hot tub?
Winter care questions
Open a question to read the answer. Everything here comes from the user and installation manual for our 7kW and 12kW heat pumps.
Should I leave my hot tub heat pump on in winter?
Yes, if you use the hot tub through winter. Left powered with the water circulating, it protects itself: if the air or water drops below 2°C while it is on standby, it heats the water back above 2°C. Our 7kW works in air down to -7°C and our 12kW down to -14°C.
How do I winterise a hot tub heat pump?
Switch it off and isolate the power, open the bypass valve and close the heat pump's inlet and outlet valves, unscrew the water connections to drain it, then close it up and fit the winter storage cover. Do this whenever a switched-off heat pump will see temperatures below 3°C.
Can I cover my heat pump while it is running?
No. Keep the air inlet and outlet grilles clear while it runs, with 1 metre clear in front of the fan and 50 cm at the sides and back. The winter storage cover is only for a heat pump that is switched off and drained.
How do I clean an air source heat pump?
Switch it off first. Wipe the casing with a damp cloth, without detergents, and clean the evaporator fins at the back gently with a vacuum cleaner and a soft brush attachment.
Does a hot tub heat pump need servicing?
Yes, once a year by a qualified person: safety checks, the electrical wiring and earthing, and the refrigerant pressure gauge.
Sources
- Outdoor Living, Hot tub and swim spa air source heat pump user and installation manual, OLHP07 and OLHP13: safety instructions, location, operation (pressure gauge, antifreeze protection), maintenance and servicing (cleaning, annual maintenance, winter storage), support and technical data, version V20221221.
- Outdoor Living, product pages for the 7kW and 12kW air source heat pumps, accessed October 2026.
Paul Margerison
Managing Director & Founder, Outdoor Living
Winter is when a heat pump earns its keep. A clear space around it, a clean filter and a yearly check keep the water hot on the coldest nights.