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Air Source Heat Pumps (ASHPs)
Last Post by GrahamF 56 minutes ago
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 Paullacey
(@paullacey)
New Member Member
Joined: 5 hours ago
Posts: 1
Topic starter 27/10/2025 8:56 am  

Hi just moved into a Barn which has underfloor heating and 2 Air source heat pumps.  We were on the understanding the one ASHP was for the underfloor heating and the other for the domestic hot water.  The whole system is operated is Vaillant with 2 panels that show how much each ASHP is drawing each day in KW and then a single digital control panel where you can alter zones and towel radiators etc. The first few weeks seemed ok although I did put up the DHW to 55 degrees as that had been set at 50 degrees and that sorted out the warm showers.  But last week we had a problem where after one shower the water was only luke warm.  Plumber came out and adjust a few things like turning off the hot water pump as this he said could be pumping water round the whole system (its a 6 bedroom barn over 4000sq ft) but that then meant the hot water tank was getting hotter but we then couldn't get hot water through.  So I turned the pump back on which solved getting hot water but then we were back to luke warm water after one shower.  So for last few days I've been turning on the immersion heater now and again so this sorts the hot water situation.

My question really relates to the 2 ASHP as we have now been told one operates the DHW and also the underfloor heating needs and the second ASHP will only come on if extra power is needed.  From my perspective is this not correct as I would have thought it would have been better to have one ASHP for the underfloor heating initially and the other for DHW and then if the first one for the underfloor heating needed extra (we have around 20 individual zones) then surely this would then draw from the DHW as that pump should not be on that much?

The plant room also seems to be constantly on with the DHW as well, so I'm assuming there must be fault somewhere as if my thinking is correct, the DHW should be stored up to temp and then only cycle is the storage falls below a certain temp.

Many thanks

Paul 



   
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 Batpred
(@batpred)
Reputable Member Member
Joined: 10 months ago
Posts: 136
27/10/2025 11:03 am  

Assuming it is your property, did the previous owners provide the instructions for it? Any diagrams or schematics you can share? Do you have details of the original installer/heating engineer that you can contact? 

Others in the forum have real experience of sizing/adjusting heat pumps, but it may also help to share the model(s) of the heat pumps, year of install if you know it. 



   
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GrahamF
 GrahamF
(@grahamf)
Estimable Member Member
Joined: 6 months ago
Posts: 83
27/10/2025 12:05 pm  

Some photos might help as well.


Grant Aerona 290 15.5kW, Grant Smart Controller, 2 x 200l cylinders, hot water plate heat exchanger, Single zone open loop system with TRVs for bedrooms & one sunny living room, Weather compensation with set back by room thermostat based load compensation


   
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