MelCloud "Mixing tank temperature"

DavidAlgarve · 2025-11-26T09:29:16Z

My buffer tank has been converted to a volumiser, but it has never been fitted with a thermocouple. MelCloud gives"Tank Temperature", which appears to be the DHW tank, but in addition it provides data for "Mixing Tank Temperature". The latter doesn't seem to vary much from 25C, so what is this connected to and can it be more usefully employed? Similarly, "Set Tank Temperature" doesn't very often vary from an unrecognisable 10C, so where is this getting its information?

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Morgan

(@morgan)

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Posts: 685

26/11/2025 3:46 pm

@davidalgarve I'm not sure that adding more and more 3rd party controllers is a good idea.

Retrofitted 11.2kw Mitsubishi Ecodan to new radiators commissioned November 2021.
14 x 500w Monocrystalline solar panels.

2 ESS Smile G3 10.1 batteries.
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DavidAlgarve

(@davidalgarve)

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Posts: 185

Topic starter 26/11/2025 3:57 pm

@morgan No they are not controllers. They are just monitoring temperatures in various rooms in the house, to give me more idea where the Mitsu Remote Controller is best located. They give a more meaningful reading than the Tado smart radiator valves.

It is made more difficult because it is an upside down house and the two main rooms downstairs (including master bedroom) are both North facing and poorly insulated, so if I locate the controller in the South facing living room upstairs, (the room you most want stable comfortable temperatures), the downstairs will be cold.

With Set temp as 22C and wireless controller reading 20.5C this is what I have right now:

This post was modified 1 month ago 2 times by DavidAlgarve

342sq m "Upside down" house in Algarve. Portugal
Mitsubishi PUHZ-120YUK 16kW ASHP
12 Solar Panels Growatt Inverter
2 x Growatt 7.5kW Batteries
Fronius EV Charger
Kia e- Niro 64kW

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Sheriff Fatman

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26/11/2025 4:05 pm

Posted by: @davidalgarve

↑

@morgan Hi Morgan.

I am struggling to keep the faith. More than a week passed and the system was learning nothing, at which point I was told that a Shelly H & T would be better than the Mitsu Wireless Controller, which had previously been said to be required.

Eventually after I decided to move the wireless controller to the coldest room in the house (our bedroom, downstairs) we saw some progress, but the target temperature of 22C was rarely met and flow temp was not as high as it might be. After buying more Shelly H & T's to spread around the house, I have chosen another downstairs room to position the wireless controller. So we are back into a learning phase and not so warm.

In addition, like you, I am getting significantly lower COP figures than previously and that is after changing the buffer tank to volumiser and deleting a pump.

I would like some relevant data to see why the disappointing performance, hence an interest in MelPump, but I can't say that I welcome using this in talking to Havenwise

This post, on my 'diary' thread, might be of interest in providing some insight into what's available from both systems. I've been using both to analyse what my heat pump is doing under Havenwise control, and the MelPump data is very useful in being able to analyse this. I'm on the free trial of Mel Pump currently, and am using it as a reporting tool only via a guest login to MelCloud set up for the purpose.

https://renewableheatinghub.co.uk/forums/postid/53010/

130m2 4 bed detached house in West Yorkshire
10kW Mitsubishi Ecodan R290 Heat Pump - Installed June 2025
6.3kWp PV, 5kW Sunsynk Inverter, 3 x 5.3kWh Sunsynk Batteries
MyEnergi Zappi Charger for 1 EV (Ioniq5) and 1 PHEV (Outlander)
User of Havenwise (Full control Jun-Dec 2025, DHW only from early Dec)
Subscriber to MelPump App data via CN105 Dongle Kit

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