Improving heat pump efficiency : circulation pump on Mitsubishi Ecodan

Sadly I have to do it on the FTC5 in the service menus.

As Rachel says, it would be good to have control over it, but all my automated controls are via MELCloud because I’m not willing to trouble my RHI / warranty.

As you say, it seems as though it would be good to slow the flow down when the dt is low.

I did try moving it down to level 1, but it caused utter chaos - the heat pump seemed very unhappy and kept cycling on and off (as you might expect). At this point I’m mostly concerned that there will be insufficient flow when it’s “really cold” (as in UK level cold) so I’ll have to manually go nudge the pump speed.

Hopefully all this experience and the information on will help people produce better heating controllers in the future and we can stop tinkering :slight_smile:

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I have this setup using a combination of Node Red and a industrial PLC - a Siemens S7-1200. I use Node red to push all the data such as Flow/Return/Outside temps along with heating mode I.e heating/hot water or antifreeze protection to the PLC via modbus TCPIP and then use the PLC to do PWM control on the pump. It is working really well. I have managed to get my Ecodan 8.5KW to tick along at between 800 and 900 Watts with very little cycling, something that never happened before I controlled the pump. When in Antifreeze mode I reduce to minimum speed which reduces consumption by over 50%



I’ve had some of these issues during my 1st winter with an Ecodan.
The issue of glycol & freezestat is covered above, but note that it also affects the output calculated and I don’t believe this can be compensated for in the FTC5 or DIP switches. I believe with 30% propylene glycol the actual energy output is about 5% less than MELCloud says.

Because then the controller can’t react to freezing conditions or any other situation. If the power is totally cut, you’d also miss firmware updates and more. Better to leave it on with a low room temperature target IMO.


Ah, by “turning it off” I was referring to the MEL Cloud operation that turns the Power flag to Off. I’m not sure that that would prevent firmware updates though it might possibly prevent an anti-freeze cycle? It obviously doesn’t cut the power completely as you can still turn it back on via MEL Cloud. I guess it’s more like a “Standby” mode.

Yep, I do that all the time.

@mjr is right, this does rely on something actively noticing that it’s become cold. I use this smidgen of code to do that:

The last time it kicked in was:

2022-12-16T06:02:07.446 INFO It’s effectively -9.55 °C outside and anything less than -8 °C is considered cold enough to turn on for

This does mean it won’t happen if the control systems are broken. Or perhaps if MELCloud was broken. In that case I would manually turn it on and it would behave in it’s normal default mode and the inefficiency wouldn’t really matter.

I can see the appeal of that. I’ve switched to doing that for the hot water (10 °C) instead of using the force and it’s been OK.

I just looked at that incidence on 16th December and the room temp was a balmy 18 °C. I’m drawing a blank on what I could set the low room temp to which would trigger it when it got cold outside. I admit it might be weird that my room temps don’t fall when the heating is off.

What threshold has been working for you @mjr ?

@MyForest I’ve rather lost the plot of your question and this is just a quick reply while at work. As mentioned in

I’m using room temperature targets most of the time now I seem to have figured out how to stop Auto-Adapt going beserk, but before that I was using 17 degrees as an “off” setting because my controller shouldn’t have ever let it get that cold unless it was in holiday mode, at which point the main controller would also be in holiday mode with a 13 degree target. I admit I was trusting the controller to run the pump if needed to protect it even when it’s not needed for heating.


No problem.

I was wondering what temperature you used to indicate “off” and you answered 17 °C. That makes sense.

Unfortunately in my case it was below -4 °C outside so I would want the system on, but it was still 18 °C inside so the Ecodan controller wouldn’t have turned the heat pump on if I set it as you did. Unfortunately it’s 18 °C inside a lot of the time so I can’t use that as my trigger.

I’ll keep pondering how to have protection against really cold temperatures whilst also pondering if it’s a good idea to turn everything completely off.

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Hi, I have 14 Kwh, PUHZ-SHW140, EHSC-VM6D and thanks to @mjr script I am monitoring it using emoncms. I also noticed that the pump1 and pump2 run if the outside temperature is < 5. I don’t have glycol in my radiators but there is no freezing danger in my house. I wonder if it’s safe for me to turn freeze stat off in installer settings. Freeze stat only circulates water in my house?

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It’ll be circulated around the outdoor unit as well.

I believe it’s necessary for the continuation of the guarantee that the antifreeze protection is enabled plus without glycol, you have the theoretical risk of damage to the HP.

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Sorry for my ignorance, there is water circulating between indoor and outdoor? I thought is refrigerant

I think monobloc pumps don’t circulate refrigerant outside the pump, making them simpler to install, so it’s water or water+glycol running to it.

I think PUHZ-SHW140 is a split unit, so does circulate refrigerant?

Thank you @mjr and @Timbones. How can I tell if it refrigerant or water circulating and ultimately if it’s safe to turn off freeze stat?

@pcman you can confirm for yourself in the data book

As @Timbones confirmed PUHZ-SHW140 is a split system.

I have a PUHZ-W112 which is a packaged unit and it has two insulated water pipes which run from the external units to supply the heated water to the indoor pipework. You should keep freezestat on if you don’t have glycol (I’m doing the same).


I took a picture of the water circuit diagram of indoor unit installation manual. My model is EHSC-VM6D so I believe it matches E*S* from this photo. My understanding is that I am running refrigerant between the inside and outside unit. Am I wrong?

The manual for the PUHZ-SHW140 does mention a refrigerant pipe…

And EHSC-VM6D is the accompanying “Hydrobox”, which monoblocks don’t have.

I’m pretty sure it is a split system.


Assuming it’a a split system, should I turn off freeze stat or there is something else I am not seeing. During winter, I have negative temperatures, sometimes -10 C

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@pcman listen to @Timbones, he knows his stuff. Turns out my packaged unit is a PUHZ-W112!

I’ll edit my original post so as not to mislead anybody else :slight_smile:


Thank you all. I turned off freeze stat and now my system consumtion is 25W when not heating

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