Do Heat Pumps Keep Running All the Time?

Very basic ASHP question(s) coming up:

Do heat pumps just keep running all the time? Can you turn the heat up and down (a bit)? Is there a thermostat that switches something off, when the specified room/area reaches the required temp?

(I understand shutting-down then starting-up again is generally to be avoided/minimised, because of wear and tear etc; maybe switch off only if going away for hols, or the like?)

Or do they just ‘self-adjust’, using pre-programmed hysteresis-loop control etc, to avoid cycling on-and-off repeatedly? Perhaps the hot water reservoir/cylinder is part of this process of evening-out the operation of the set-up?

Heat pumps are best left switched on all the time but they only run as required and at the appropriate modulation.

If your heat pump is only for space heating you can leave it off during the summer.

In this respect they are the same as correctly set up boilers.

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Hope this helps.
As you can see our ASHP runs up to typically 19hrs/day on-time (in winter).
All of this happens automatically under weather compensation control with room thermostat influence (on top of the weather comp).
It is probably worth noting that someone is effectively at home all day at our house so these extended on-times are the way we prefer it to run, but if you were out for (say) 0800-1800hrs then you could adjust a set back period to reduce the extent the system runs while you are out.
The system goes “off” when the outside temp averages greater than 15C over a few hours (both the threshold and averaging period can be adjusted). This pretty much deals with the summer months and keeps the system off in terms of space heating but obviously the hot water remains “on”. Although clearly the hot water demand is such that the number of hours needed is very small.
There is also a holiday mode which turns the whole thing to standby mode / off. The holiday mode can set to a calendar / timer so that it goes into holiday mode while you are away and comes back on timed with your return. It is also accessible via a web app so if you are returning at an unplanned time/date you can turn it back on anyway.
All of this will partly depend on which model of HP you choose and what control options are available - but this is now pretty typical I think.


This HP person is experimenting with turning his off…

Graham Hendra turns off his HP in summer

Thanks everyone. Would it be a reliable subjective test of heat-pump-readiness at our house (3-bed semi) to
*install two or three large-area radiators, at least in the main downstairs areas
*drop flow-temp on our existing gas boiler to, say, 50deg or 45deg (I ran it last year on 53deg, seemed fine)
*see how that feels (to all 3 of us…!) re space-heating, over the coming winter?

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That is roughly what I did. I had already installed larger than “necessary” radiators in most rooms and gradually reduced my boiler flow temperature to 40°C. Last winter there was a week when I needed to up the temperature to 45°C. SE England climate zone. I could have made further improvements before ditching the boiler but the BUS turned up and my boiler was older than it’s predicted life so I bit the bullet. I can still make improvements to my home and reduce the heat pump flow temperature to improve COP.

As I could demonstrate that my radiators and hot water cylinder functioned at low Δt I was able to avoid other “improvements” and just pay for the heat pump and ancillary controls plus installation.

For reference, 6kW Daikin with fitting was £9000, less BUS of £5000, so £4000 all together. And the cost of a pre install EPC to qualify for the grant as previously the building hadn’t had one. That’s for an enhanced 4 bed semi with “solid” masonry walls. The old boiler was 41kW.

It took a lot of shopping about to get the system I wanted without the installers insisting on £1000s in extras.


Thanks Tim, very useful.

Tim, that was a very useful answer, “without installers insisting on £1000s in extras” is where I seem to be at present (hence my researching ZEBs).