Thermostat recommendation please

[Norbert77]

Hello all, my dad had a heat pump installed last year and it works just fine till a bit below freezing, about -12 celsius, what happens is too often the auxiliary is called for. Basically it starts, takes a while to warm up because it is a inverter DC setup and does it's thing slow, then runs 15 minutes and thermostat switches to auxiliary. I tried the slow/med/fast adjustment, seems to run out longer but the aux still kicks in

 

[John Gayewski]

Hello all, my dad had a heat pump installed last year and it works just fine till a bit below freezing, about -12 celsius, what happens is too often the auxiliary is called for. Basically it starts, takes a while to warm up because it is a inverter DC setup and does it's thing slow, then runs 15 minutes and thermostat switches to auxiliary. I tried the slow/med/fast adjustment, seems to run out longer but the aux still kicks in

If it's too cold outside the heat pump can't pump enough heat to heat the structure. Rather than run ineffectively, the heat pump should switch into electric resistance heating or auxiliary heating mode. Are you saying that your heat pump should run in heat pump mode below - 12? Most can't effectively heat at those temps.

If you've had this installed recently then you need to contact the installers and tell them you don't think it's working correctly.

 

[Sponsor]

 

[Fitter30]

Brand and model of thermostat. Model will on the thermostat portion or subbase.
Outside unit brand and complete model?

 

[Reach4]

1. Consider turning the temperature setting to close to the current temperature for a while. That may cause the aux heat from turning on prematurely. Does this unwanted aux heater only come on when the thermostat setting has been raised, or does it happen when the temperature setting has been held the same?

2. As Fitter30 said, check the setting on your thermostat documentation. For example, https://diy.stackexchange.com/questions/239864/thermostat-keeps-switching-on-aux-heat-unnecessarily discussed settings for a particular thermostat.