Hitachi Yutaki SCombi Heat Pump - Thermal Off's

trebor12345 · 2025-04-06T20:53:42Z

I posted a few days ago to see if there were any owners of the Hitachi Yutaki SCombi Heat Pump. It seems it's a rare beast. I wanted to find out from other users their experience of this equipment. Having not found anyone, I thought there may be value in posting my issues. I have to add, I new to heat pumps and do not have assess to quality performance reporting statistics/equipment. So here goes: System 2024 build bungalowMoved in 9 months ago200m2High level of insulationUnderfloor heatingAll 12 circuits are fully open all the time1 thermostat in family room3kw heat pump50 litre buffer tank Heat Pump Model No. (Indoor Unit ) RWD-3.0RW1E-220S-KHeat Pump Model No.(Outdoor Unit) RAS-3WHVRP1 Comments Unable to run the system 24/7 as the house gets to hot (24C overnight in the bedrooms) I am only able to monitor the system (i) via a temperature probe fitted to the Gas Flow pipe into the indoor unit. (ii) via an energy monitor. The energy monitor shows when the heat pump switches on and off and when it performs a de-ice. I have attached the result obtained of the gas temperature probe. The graph shows that there is "thermal off period" (that’s how Hitachi describe it), when compressor goes off – draws no power and then 8 minutes later the system conducts a de-ice. This thermal off period and then de-ice is so repeatable, different days, at different flow temperatures and different outside temperatures. Why does the heat pump perform a thermal off period and then 8 minutes later a de-ice (and do it so consistently. Does this performance indicate anything wrong with my system? I appreciate I may not have given all the info required, but this is a stating point. I have also attached an image of the internal unit

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JamesPa

(@jamespa)

Illustrious Member Moderator

12249 kWhs

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Posts: 2292

08/04/2025 8:57 pm

Sorry I cant help further. Knowing when the various components (compressor, fan, EEV, water pump) change state might illuminate the matter, but otherwise its presumably just a sequence devised by some Hitachi engineer.

4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.

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trebor12345

(@trebor12345)

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199 kWhs

Joined: 1 year ago

Posts: 16

Topic starter 08/04/2025 10:07 pm

Thanks for your help.

Hitachi Yutaki SCombi Heat Pump
(Indoor Unit ) RWD-3.0RW1E-220S-K
(Outdoor Unit) RAS-3WHVRP1

2024 build bungalow
Southern england
200m2
High level of insulation
Underfloor heating
All 12 circuits are fully open all the time
1 thermostat in family room
3kw heat pump
50 litre buffer tank
3.6KW solar panels