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Heating Turned Off but Radiators Still Warm

Air Source Heat Pumps (ASHPs)

Last Post by DREI 7 months ago

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Pipcart

(@pipcart)

Eminent Member Member

Joined: 3 years ago

Posts: 23

Topic starter 08/03/2023 6:40 pm [#877]

Can anyone shed any light on why our Daikin Altherma 3 Monobloc (R32) should still be keeping the radiators warm and the hot water above target temperature, when everything is switched off?

While we have builders working on our house and some of the windows are replaced by boards, I want to maintain it at a safe level to avoid freezing, but no more.

The heating is set for constant a water temperature (not weather dependant) of 35C and the thermostat set to 5C. However, when there was nobody there yesterday, my temperature loggers show that the house was kept between 12.5C and 13.9C. The DWH is set to 30C, but has been maintained at 36C.

Our installers tell me that the system is still running to protect it from the current cold weather. However, even when the outside temperature was at least 5C, the compressor was drawing an average of 1.142 kwh.

This morning, the forecast said that the weather would not freeze, so I turned off both the heating and DWH. However, the compressor has been running most of the day and the radiators are still warm.

When we are living in the house, this behaviour would not matter, but I am keen to understand what is going on, in case it reveals a fundamental fault in the system. I would also like to stop paying to heat the garden!

Does this match the behaviour you would expect in colder weather? Would the cold weather system protection require the house to remain warm?

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heat pump cold weather

9jwr9

(@9jwr9)

Active Member Member

Joined: 7 months ago

Posts: 9

11/10/2025 8:05 am

Did you ever get an answer to this? I'm experiencing the same thing!

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JamesPa

(@jamespa)

Illustrious Member Moderator

Joined: 3 years ago

Posts: 4799

11/10/2025 9:33 am

Posted by: @9jwr9

↑

Did you ever get an answer to this? I'm experiencing the same thing!

What do you mean by 'turned off' exactly. Same question to @pipcart.

Unless you cut the power completely:

Most if not all heat pumps (and so far as I know boilers) will come on at about 5C to prevent freezing
If you have a buffer between heat pump and emitters the heat pump may, depending on how it has been wired, try to keep the buffer warm even if there is no call for heat from the heating.
If you haven't got a buffer the heat pump will output water at the chosen flow temperature unless you specifically tell it not to or it is set up to react to a call for heat which is off
Many heat pumps and boiler controls that apparently have on/off are actually on/setback, with setback being typically a few degrees cooler.

Which of these if any apply and have you got a buffer?

This post was modified 7 months ago 2 times by JamesPa

4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.

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Pipcart

(@pipcart)

Eminent Member Member

Joined: 3 years ago

Posts: 23

Topic starter 13/10/2025 5:53 pm

@9jwr9 I didn't get an answer at the time and there has been so much water under the bridge since then that I can't remember the details. Hopefully JamesPa will be able to help you. Goog luck!

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DREI

(@drei)

Estimable Member Contributor

Joined: 9 months ago

Posts: 98

14/10/2025 1:51 pm

Posted by: @9jwr9

↑

Did you ever get an answer to this? I'm experiencing the same thing!

I love Necromancy... but to follow James, heat pumps WILL heat your water and radiators even if you don't feel it, the difference between a system switched OFF and ON, is that your radiators would actually become COLD, where a heat pump will keep them at room temperature, and you won't be able to tell the difference.

As James stated, unless you switched it OFF from the control menu, or by using the isolator switch, then it is working gently in the background.

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