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Hitachi split ASHP issues

 
Air Source Heat Pumps (ASHPs)
Last Post by trebor12345 4 weeks ago
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 besidethewye
(@besidethewye)
New Member Member
Joined: 4 weeks ago
Posts: 3
Topic starter 28/03/2026 5:23 pm   [#2915]

Hi there - new member on here.  

We have a Hitachi split system - Yutaki RWM-4NE/RAS-4WHVNPE - nominally 11kW output.  

It was installed after Western Power would not accept the Panasonic T-cap we had before (and which appeared to work well).  The installers appear not to have programmed it - it cycled like mad and eventually (with the help of Hitachi) I found that it was not set to respond to the room thermostat so the pump was on and off as the buffer tank got to temperature - ie a lot.

We are in the process of sorting a new UFH circuit which has me looking at the HP again.  

It has never seemed to work well - much less cycling after I found the way to link it to a room thermostat to call for heat but still not good.  The house needs very little heat (but the new circuits will take more).  So I assumed at least part of the problem was a big heat pump and small heat demand.  

Even with the new circuit in I don't think total load is going to be much above 6kW (begging the question why the installer put in such a big system).  

I think a good part of the problem is a mismatch between flow from the heat pump to the buffer tank and flow in the heating circuits.  The heat pump tells me that the flow to the buffer is 1.8m3/h - on the outlet side the total flow will depend how many circuits are calling for heat but the UFH loops are around 1.5l/min each and typically there would be three running - the new area will add another 4 - but total flow is still only 0.5m3/h if my maths is right.  

 

I rather assumed the heat pump circulating pump would modulate but it always seems to be on the same (and it is set to 50%). 

 

There is little in the manual that enlightens me.  The original installer simply said 'we would not do that' and refused any assistance.  A service engineer achieved nothing other than putting the system out of action by disturbing a connection.  

Any advice would be gratefully received.

 

Cheers and thanks



   
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trebor12345
 trebor12345
(@trebor12345)
Estimable Member Member
Joined: 2 years ago
Posts: 147
28/03/2026 8:20 pm  

I also have a Hitachi split system similar to yours, details in the tag line.  I also had a lot of problems with cycling, the principal reason being that the heat pump is oversized by a factor of at least 2 for the property.  There are also a number of other issues, which over the last 2 years I have fixed.  One problem that I cannot fix, is that of the type of property, it’s approaching Passive, and only needs little heat - 2kw at -2C.  The heat pump installed is around the 7kw mark.

When I arrived at the bungalow the system was never set-up properly, flow set 42C, actuators on all the underfloor heating circuits, UFH not set up, 11 room temperature stats, contaminant in the UFH, etc.  Hitachi were called in to commission the system, but they didn’t appreciate the passive nature of the building and that the heat pump was oversized, so not a lot changed.

Buffer tanks, you will hear from many others on this forum, should a system have one?  I do and it’s part of my problem.   Over this winter I started to appreciate that the flow rate out of the primary circuit needed to match that of the underfloor secondary circuits.  With the help of 4 temperature probes I was able to get close to balancing these 2 flow rates.  In the attached image you will see that mixing is still occurring in the buffer tank, in the order of 1C, this was the best I could achieve.  The result effect is that I am wasting energy, and the return to the heat exchanger is being increased by 1C by the buffer tank, so also loosing efficiency. Also making thermal cycling worse.

There is a setting in the Installer Access where you adjust the primary pump speed, I currently have about 1.4 m3/hr on the primary and 23 l/min across my 11 underflow circuits.  The underfloor is fully open with no wall thermostatic controls.

I had horrendous problems with cycling to the extent that the system would turn off and on every 3 minutes. After a winter season of complaining, Hitachi came up with a SW fix that works for me (could work for you).  The SW measures the flow temperature returning to the exchanger, takes a snap shot of this, and once the temperature reduces by a set value (1c, 2C, 3C, 4C) the heating is turned back on.  This works for me as the heating will turn off anywhere between 1 or 2 hours, thus limiting the amount of heat being pumped into the building.

Defrost cycles were also a problem, the system performs a defrost even with outside temperatures of 13C. Once again there is a SW setting for this.  The settings appear to be every 30 minutes or 43 minutes.  With 30 minutes it defrosts at OAT of up to 13C.  With the 43 minute setting, the exchanger coil on the heat pump goes into stagnation where the ice build up is so significant the output temperature of the HP drops by up to 3C.  Not sure if this is relevant to your issues, so can provided more detail if needed.

I have a collection of Hitachi technical/service manuals which might be of interests if there are some similarities in our systems.

Going forward I am having the system taken out and replacing it with a Vaillant, of only 3.5kw. Reason why, it does not fit in this type of property and does not meet my future needs.

IMG 3754
IMG 3753

 

 


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

2024 build bungalow, Southern england, 179 m2, 14w/m2
Underfloor heating all fully open
7KW heat pump
50 litre buffer tank (4 port)
3.6KW solar panels


   
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 besidethewye
(@besidethewye)
New Member Member
Joined: 4 weeks ago
Posts: 3
Topic starter 29/03/2026 10:09 am  

@trebor - thanks very much for all that - does sound like we have a few issues in common!

The sizing must be at the base of it, compounded by a failure to set it up.  

To be fair the building is very tricky - we really only need heat in two rooms - most of the building is near passive but we have an old part that is not (by miles).  We might be better with two systems really (hindsight being a useful thing).  

I need to understand the defrost cycles better - we only ever run the system overnight on low rate electricity so I miss a lot of what is going on!  The unit cycling is definitely better for using the call for heat from the thermostat.  

Sounds like I was on the right track on the buffer - I will struggle to get it balanced - partly because I can't get enough water out of it into the system (unless I can throttle the HP back a good deal) but also because the amount going out is dependent on the call for heat and the different parts of the building behave very differently.  Some sort of bypass circulation might help on the flows if not on the efficiency perhaps.  

Thank for the pointers on the software and controls.  Let me see what I can do.

How did you get to someone who took an interest in Hitachi?

Thanks



   
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trebor12345
 trebor12345
(@trebor12345)
Estimable Member Member
Joined: 2 years ago
Posts: 147
29/03/2026 3:32 pm  

Posted by: @besidethewye
↑

@trebor 

How did you get to someone who took an interest in Hitachi?

Thanks

Are you refering to the builder who installed the system or someone from Hitachi to come and fix issues/install new SW?

 


This post was modified 4 weeks ago by trebor12345

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

2024 build bungalow, Southern england, 179 m2, 14w/m2
Underfloor heating all fully open
7KW heat pump
50 litre buffer tank (4 port)
3.6KW solar panels


   
ReplyQuote
 besidethewye
(@besidethewye)
New Member Member
Joined: 4 weeks ago
Posts: 3
Topic starter 29/03/2026 6:32 pm  

@trebor12345  I was thinking, from what you said, that you had got onto someone at Hitachi



   
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trebor12345
 trebor12345
(@trebor12345)
Estimable Member Member
Joined: 2 years ago
Posts: 147
29/03/2026 8:52 pm  

Posted by: @besidethewye
↑

@trebor12345  I was thinking, from what you said, that you had got onto someone at Hitachi

I will send you a PM.

 


This post was modified 4 weeks ago by trebor12345

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

2024 build bungalow, Southern england, 179 m2, 14w/m2
Underfloor heating all fully open
7KW heat pump
50 litre buffer tank (4 port)
3.6KW solar panels


   
ReplyQuote



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