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Daikin Altherma 3 H HT - Freeze Prevention Threshold

Air Source Heat Pumps (ASHPs)

Last Post by RICHARDF5033 3 weeks ago

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RICHARDF5033

(@richardf5033)

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Joined: 3 weeks ago

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Topic starter 18/02/2026 12:34 pm

Hi. We have an Altherma 3 HT (18kW I think) which, now we've completed a load of tweaking, gives a SCOP of around 3.6. It is used in a single storey barn conversion with a lot of vaulted ceilings (not great), and underfloor heating system. Because it is single storey, it is 'long and low'. As a result, when the system was installed 14 years ago, it was fitted with pipe freeze prevention valves rather than adding glycol (I guess over concerns of the glycol reducing the heat-carrying capability of the water over the 45m run to the farthest room). This causes a problem on cold but sunny winter days. Because the house benefits from a lot of solar gain, the stats will frequently switch off and the heatpump stops. But because the pump isn't running and the water in the system doesn't have glycol added, the system protects the external pipes from freezing by taking heat from the hot water tank causing either a huge drop in water temp, or excess electricity usage to keep reheating the water. What troubles me most, is that this Pipe Freeze Prevention cycle kicks in when the outside temperature drops to 6.9 degrees centigrade. This seems excessively high and dictates that any sunny day from late autumn to late spring means we have to have heating running whether the house needs it or not. My question therefore is; is 7 degrees the correct threshold? Our engineer is stumped as he has found a setting which "appears to be" the threshold for the freeze protection, currently set at 7, but on the Daikin app shows as a default of 3. (It is setting 407). The problem is, it is the only setting that doesn't have a title/explanation within the app! Can anyone confirm what level the Pipe Freeze Prevention threshold should be set at by default and if 407 is the appropriate setting please? Cheers.

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