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Replacing my 18 month old Hitachi Yutaki ASHP

trebor12345 · 2025-11-23T14:54:01Z

I am perhaps looking at replacing my split level ASHP. What is the best premium brand to replace with (Dakin comes to mind)? Maybe I would like to keep it as a split level system. I am also considering going back to gas, but don’t have a gas supply to the property. So looking into that as well. Why do I want to do this? Oversized HP, too many thermal offs, bungalow not warm on cold days due to defrost cycles, requires constant management to maintain house temperature. My wife would not be able to manage the system if I was not here. The bungalow spec is as the tag line below. (PS, as an example, had a thermal off this morning, was 3 hours before the system came back on. Back on for 1 hour, and not back on after 2 hours.)

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Air Source Heat Pumps (ASHPs)

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trebor12345

(@trebor12345)

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Topic starter 28/11/2025 10:36 am

Posted by: @robs

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Posted by: @trebor12345

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Water comes out of 2 holes in the bottom of the heat pump. One in the middle and one to one side.

There is no pipe.

Thanks, if the water can drain out of the heat pump without any issues in sub-zero temperatures then that's one possible issue ruled out.

But if the water doesn't run away and collects under/beside the heat pump then it will increase the humidity around the heat pump which isn't ideal and will increase the frequency of defrosts needed.

It the last cold spell, there was a thin layer of ice under the HP (about 3mm thick). Based on my measurement that each defrost cycle produces 1 litre of water, thats 10 litres overnight (2 black water buckets). So that does go somewhere.

So and my assumption, there is about 1 litre of water under the HP. Do I need to do something about this?

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

2024 build bungalow
Southern england
179 m2
High level of insulation
Underfloor heating
All 12 circuits are fully open all the time
1 thermostat in family room
7KW heat pump
50 litre buffer tank (4 port)
3.6KW solar panels
Energy used by heating 2527 KWh - 7527 KWh (SCOP 3.5 approx)

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JamesPa

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28/11/2025 10:49 am

Posted by: @trebor12345

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So and my assumption, there is about 1 litre of water under the HP. Do I need to do something about this?

Not unless its obstructing water coming our or causing a slip hazard.

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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Topic starter 28/11/2025 10:49 am

Posted by: @jamespa

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Posted by: @trebor12345

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As you can see from the picture there is about 4 inches between the HP and the plinth.

It looks like the 2 holes are just holes in the metal casing, no fancy heating.

All helps build a picture. The hysteresis (4C you said) on the 'thermal off' is, I fear going, to work out too big when the FT is low (ie in warmer weather). No idea exactly where this is set but its in one of these menus! I wouldnt suggest changing it yet but it may need to be changed. When its warm you are likely to be running at an FT of 23-25 to achieve balance of heat lost and heat added. Waiting for that to drop by 4C before the heat pump turns on is unlikely to work.

From memory of conversation with Hitachi, it's not a setting in the SW, it's a manual configuration of the buttons and switches on the control boards.

When its warm like yesterday, I just run for the heating for 3 or 4 hours.

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

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trebor12345

(@trebor12345)

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Posts: 80

Topic starter 28/11/2025 10:52 am

JamesPa

This yesterdays run. In manual mode, so I turned the heating off and on. It was 13C OAT yesterday. But the off cycle between 6 and 10 was the Thermo Off cycle.

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

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JamesPa

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28/11/2025 11:00 am

@trebor12345

Well that is interesting. Note that even without defrost the FT fell to ~28 overnight.

I now suspect you have a setback operational. What I dont understand is the slow tail off, but maybe this is just the control system and the slab slowly cooling.

Its even possible that the setback alone is the cause of the observed reduction in FT during defrost, and that night shift isnt making a difference to this. I think I would leave night shift on for now, but cancel the setback. That way we can work out whats happening for definite.

This post was modified 13 minutes ago by JamesPa

This post was modified 7 minutes ago by JamesPa

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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JamesPa

(@jamespa)

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28/11/2025 11:02 am

Posted by: @trebor12345

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From memory of conversation with Hitachi, it's not a setting in the SW, it's a manual configuration of the buttons and switches on the control boards.

Thats a shame if its true. However there are some parameters on the controller that seem to relate to this, I pointed to them a few posts back. Capturing their current values will hopefully clear the matter up.

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

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Topic starter 28/11/2025 11:11 am

Posted by: @jamespa

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Posted by: @trebor12345

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From memory of conversation with Hitachi, it's not a setting in the SW, it's a manual configuration of the buttons and switches on the control boards.

Thats a shame if its true. However there are some parameters on the controller that seem to relate to this, I pointed to them a few posts back. Capturing their current values will hopefully clear the matter up.

I have been in the system and done some images of what I found. Not the same as your details. I didn't find an ECO setting.