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Help me understand my Mitsubishi Ecodan system

GergoH · 2025-04-24T01:00:57Z

Hi everyone With my new house came a nice and shiny Mitsubishi Ecodan air-to-water HP system with it's UFH (and ceiling) loops, buffer tank, valve actuators, zone controllers, circulation pumps and all bells and whistles. The only problem is: it's not very efficient + it short cycles like crazy. I'd like to get things in to improve it as much as I can but there are few conflicting information that I don't quite understand yet. First, by monitoring the flow and return temps it seems to me that the heat pump doesn't really care about the buffer tank at all just provides a more or less constant flow temperature around the setpoint until it reaches about setpoint+2 C°, at which point the compressor stops and then starts again after few minutes starting from setpoint again. Strangely (or maybe not) it doesn't even have sensors past the box, so all it sees are the primary flow and return temperatures. I've read from multiple sources that the buffer tank should help avoid short cycling by storing some of the heat but I don't really see it happening here with this 2 C° delta. But anyway, let's go further. It's not a good idea anyway to use the buffer tank for storing heat, right? So I read that it'd be more efficient to match flow rates in and out of the buffer to avoid distortion and disturbance of the water inside for optimal efficiency. I can kind of see that by putting in some effort I might be able to match that 25L/min flow that I can read from the heat pump. What it would cost is having a constant pressure, constant rate setup and losing all dynamic control. BUT it would be doable... for the winter. For summer however, when cooling kicks in I don't see how this would be viable at all: there's excessive solar gain on one side of the property in the morning and on another side in the afternoon, which means I need dynamic control. There's also the dew point to take into account for cooling so the mixing valve after the tank is absolutely necessary, which will decrease the flow from the tank, worsening the balance. So to summarize: I can't really see myself going the balanced/open-loop route but maybe I could, I'm just overcomplicating it (?). On the other hand currently the heat pump doesn't seem to store any usable amount of heat in that buffer tank and it short-cycles a lot, so that's also not great. I've talked to the installer who recommended a device that disables the heat demand signal if it detects overly frequent compressor starts but to me that seems like we are only treating the symptom.Do you think everything is in order and I'm just chasing shadows or is there something I could do to improve the situation?

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Air Source Heat Pumps (ASHPs)

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Carpenterstation

(@carpenterstation)

Trusted Member Contributor

Joined: 2 years ago

Posts: 49

25/04/2025 12:25 pm

@abernyte nope.

I have an “actions”, “All off” option top right of the “building list” page but that turns off Hot water too, and there is an “on / off” option on the building itself top left. But again this turns off hot water too. See attached? Is this normal?

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Gary

(@gary)

Reputable Member Member

Joined: 4 years ago

Posts: 350

25/04/2025 1:03 pm

@carpenterstation Yep that looks all normal, if you want to turn the heating off and leave the hot water on then you have to do it from the controller.

You could sign up for Melpump its a web app that gives you some further control. The first month is free then annual subscription is currently £26 you also need an additional wifi adaptor that is £30

This would allow you to disable the heating from your phone and leave the hot water active

https://melpump.com/

👍

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Carpenterstation

(@carpenterstation)

Trusted Member Contributor

Joined: 2 years ago

Posts: 49

25/04/2025 3:20 pm

@gary another £50 … in addition to the £several hundred to measure actual energy used…. Why is none of this standard?

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Gary

(@gary)

Reputable Member Member

Joined: 4 years ago

Posts: 350

25/04/2025 3:28 pm

@carpenterstation because heat pumps are built by engineers and have not been historically developed for the average human to be able to operate, hence, the reason this forum exists.

Yes that needs to change but its not going to be a quick process, this isn't a Mitsubishi specific issue its an industry issue.

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RobS

(@robs)

Estimable Member Member

Joined: 2 years ago

Posts: 138

25/04/2025 3:41 pm

@gary

Posted by: @gary

↑

@robs Is this only in the newer controllers I don't have that option on my FTC5

The FTC6 and FTC7 both have summer mode.

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Gary

(@gary)

Reputable Member Member

Joined: 4 years ago

Posts: 350

25/04/2025 3:48 pm

@robs Thanks that's what I suspected mine definitely doesn't have it.

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RobS

(@robs)

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Joined: 2 years ago

Posts: 138

25/04/2025 3:52 pm

@carpenterstation

If you don't want to use summer mode ( https://renewableheatinghub.co.uk/forums/postid/45608/) then you could slide the zone set temperature sliders to their minimums in MELCloud to turn off heating without turning off DHW.

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Carpenterstation

(@carpenterstation)

Trusted Member Contributor

Joined: 2 years ago

Posts: 49

25/04/2025 4:35 pm

@robs Sorry to ask silly questions, but how do I access the “service menu under operational settings” on the controller? I have searched on YouTube without success for “summer mode”?

the only option I can find on the FTC under operational settings in the service menu is “System shutdown” ? I must be looking in the wrong place ?

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RobS

(@robs)

Estimable Member Member

Joined: 2 years ago

Posts: 138

25/04/2025 6:37 pm

Posted by: @carpenterstation

↑

the only option I can find on the FTC under operational settings in the service menu is “System shutdown” ? I must be looking in the wrong place ?

@carpenterstation

When changing settings in the service menu you often need to shutdown the system first, so if it's running it'll ask you if it's okay to shutdown and afterwards it displays the settings you can change.

👍

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