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Hoped for improvements not being realised on my Mitsubishi heat pump

DavidAlgarve · 2026-01-30T17:22:00Z

I didn't think I had too many problems with my Mitsu last year operating on weather compensation, but based on topics here, I was convinced that I could improve the performance by converting the buffer tank and switching to Adaptive with a PAR 60 Wireless controller. So I started this season with the mods completed and using the HavenWise version of adaptive. After a few weeks trial, I was not getting the same comfort levels and the reported COP was less than last year. I had no ability to analise why the expected improvements were not being realised, so I decided to suspend use of HavenWise, go back to weather compensation and sign up for MelPump. I have attempted to optimise weather compensation like i did last year, but although I am getting similar COP figures (3.0 to 3.6) i am struggling to get 20C in my downstairs rooms and 21.5c upstairs, with ambients of say 10C and this had not been a factor last year. MelPump report an "Energy efficient House". I have played with weather compensation (currently 27C @ 18C and 45C @ -1C) and flow rate (tried 3 & 5) and have failed to increase available room temperatures. I am unsure if I am correctly interpreting the MelPump data and I am particularly concerned at the "saw tooth", stop start, nature of the temperature report which I am attaching below. I would appreciate any advice/ comments on where I should concentrate further tuning to improve comfort level and smooth out the heat pump output.

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Air Source Heat Pumps (ASHPs)

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JamesPa

(@jamespa)

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Joined: 3 years ago

Posts: 4864

13/02/2026 6:02 pm

Posted by: @davidalgarve

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but it will probably be worthwhile to box it in with additional insulation in view of the higher temperatures.

Once its all working then maybe yes. Hopefully the re-pipe will reduce the flow temperatures needed!

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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smsm1

(@smsm1)

New Member Member

Joined: 3 months ago

Posts: 5

13/02/2026 11:29 pm

Posted by: @davidalgarve

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The Grundfos pump is showing a green LED which on some models of the UPM3 indicates "No external control", but I can't think that applies in my case where the flow changes when the pump speed is changed from e.g. Setting 3 to 5.

Steady green means that the pump is running full speed. If you slow the pump down, then it'll start flashing due to the PWM signal. Speed 5 is the top speed and no PWM.

On the Havenwise and the Shelly thermostat, do you run the thermostat on battery or USB power? I had problems running it on battery as the updates to the temperature were way too slow like every half an hour max with Havenwise adjusting the flow way too quickly as it was upping the flow temp and not seeing an effect from that, when on USB the updates are much quicker, and so it sees the effect much faster thus able to get the right flow temperature.

This post was modified 3 months ago by smsm1

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DavidAlgarve

(@davidalgarve)

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Posts: 244

Topic starter 14/02/2026 6:47 pm

@smsm1 Thanks for your interest.

At the time that I lifted off the PCB to get to the pump, I was on setting 5 and I haven't checked at lower settings because I need everything I can get from the pump! I suppose "No external control" could mean "no PWM"

When I was using Havenwise I was using the Mitsu PAR-WT 60 wireless controller and only using a number of Shelly Gen 3 devices to check on individual room temperatures and they are all using battery power.

However, I have abandoned Havenwise and 'adaptive' and reverted to weather compensation. Your explanation is probably one reason why Havenwise just didn't seem to be capable of working for me, although the layout of the house is also an important factor.

Havenwise did ask if I would use a Gen 3 for control, but I think even they were not confident that it was a solution.

342sq m "Upside down" house in Algarve. Portugal
Mitsubishi PUHZ-120YUK 12kW ASHP
12 Solar Panels Growatt Inverter
2 x Growatt 7.5kW Batteries
Fronius EV Charger
Kia e- Niro 64kW

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smsm1

(@smsm1)

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15/02/2026 4:13 pm

Posted by: @davidalgarve

↑

I suppose "No external control" could mean "no PWM"

Yes it does, I've confirmed this on my own unit when I changed the pump speed. Due to the low loss header on my pre-plumbed unit and 6KW outdoor unit, I've gone for a low flow speed to the outside unit, and high speed to the radiators, which has improved the COP somewhat.

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