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DHW heat loss through pumps.

ngillam · 2025-11-18T14:33:27Z

Hi all, I have an Ecodan 5kw ASHP with 210litre pre-plumbed DHW tank, we live in a very well insulated new build on a very exposed hill but our COP is 4.9 with heating on 24hrs so all good on that front. The next challenge now we have a cold spell is the best way to set up the DHW supply to taps and shower, we heat to 47degs with a drop of 5....if I leave the Heatmiser timers off the water stays hot all day/night, if I leave them on (for constant HW demand) then the heat dissipates over a few hours meaning low temp for showers when we need them. We've started switching the timers on as soon as we want showers but this drops the temp by 4 degrees or so as I assume it "fills the system" and with the colder weather it dropped to 38 this morning with combined timer switch on and ASHP defrost. We both love hot showers twice a day but we feel we're compromised and would like to get the best set up even though it'll cost us a little on COP. Does anyone have an idea on how to get around this? The other half doesn't like having to set the timer to 30 mins for shower....she often forgets in the morning....I can hear her tutting as I write this. Thanks Neil.

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Domestic Hot Water & Cylinders

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ngillam

(@ngillam)

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Topic starter 22/01/2026 10:41 am

@marzipan71 Ah yes.....I see you've given this a lot of thought. 10 year olds leave lights on too, or mine did.

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Marzipan71

(@marzipan71)

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22/01/2026 11:13 am

Posted by: @ngillam

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@marzipan71 Ah yes.....I see you've given this a lot of thought. 10 year olds leave lights on too, or mine did.

Ah - you just hit on a problem - the boy has a switch in his bathroom for the recirc pump - on is no problem, but turning it off is another matter entirely. Motion sensors in the shower cubicle!

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JohnnyB

(@johnnyb)

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25/01/2026 11:58 pm

Posted by: @jamespa

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That will probably help but does of course mean that the water which was piping hot at the top is returned to the top slightly cooler, as a result of being circulated.

It did cross my mind but I'm trying to ignore that so please don't remind me 🤣 Hopefully the loss will be very small. I will try it once the house if finished, but that is a long way off.

Posted by: @marzipan71

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My ramblings about the shower valve being wifi connected - you made me think @johnnyb that it might be possible to install a switch either in a spare slot in my wall switch or a wireless switch that could tell a digital timer (rather than the mechancial timer I currently have) to swtich on or off. Would need one in my son's bathroom also. I'm not in any way electrical so not sure if that exists but my experience is that if you can imagine something wifi or smart, it probably exists.

That is what I was wondering about as well. My son's are old enough to think about switching the pump on if I make it simple for them and the water runs hotter. Reading the first page I see that @ubert767 included a link to a switch at toolstation that does what we want, and if I understand it correctly there can be several switches connected to one receiver, so one in each bathroom shouldn't be a problem