Conflicting thermostats - Ecodan Heatpump

Hi All,

I’ve just had my new heating system installed and commissioned -

  • Mitsubishi Ecodan Air source heat pump
  • Underfloor heating system with Salus controls

So I effectively have two thermostats - the heatpump has its room thermostat, and the UFH has a thermostat. The hot water cylinder and heatpump controller are located in the loft, as I do not need regular access to these and it saves space. However, I didn’t initially realise that the heatpump had its own thermostat control for room temperature, so as it was left by the installer I had the following scenario:

  1. Heatpump thermostat in loft (where there is no heating) set to 20 deg.
  2. UFH thermostat in room set to 18 deg.

My understanding is that the heatpump would be trying to satisfy both of these demands - 1. is effectively impossible as there is no heating in the loft. So initially the energy demands were rather higher than expected…

I have since set 1. to its lowest temperature setting (10 deg), so my understanding is that the system will now be solely controlled by the UFH thermostat (which will eventually be added to my Home Assistant config).

The heatpump is now behaving more as I would expect, but just wondering if I am understanding the situation correctly and if anyone has any better advice.


Hello Andrew

The EcoDan controller can be used in 3 main modes:

  • room temperature auto adapt
  • fixed flow temperature
  • weather compensation

With the EcoDan controller up in the loft, the most efficient way to run this (without moving the controller) is to set it to weather compensation and adjust the weather compensation to match your system design.

To begin with set the UFH thermostat 1-2 degrees above the temperature that you would like to target and keep adjusting the weather compensation settings on the main controller until the system essentially achieves the target temperature that you are after just by running the water temperature in the system at the right temperature.

You want to use the UFH thermostat more like an overheat cut off rather than your main source of temperature control. If you get the weather compensation right that should keep your house at a nice even temperature with the lowest flow temperatures possible - ensuring efficient operation.

Personally though I would get the main controller moved to your main living space so that you can more easily adjust the settings rather than having to go up to the loft. You could then experiment with using the auto adapt setting and all the scheduling options build into the Ecodan controls - which may help you tweak the system for better performance.

Do you have multiple UFH thermostats and zones? or is it just the single thermostat turning all circuits on/off?


There are a couple of videos on youtube that go over how to set the weather compensation curve on an Ecodan, here’s one example How to change your heat curve for your Ecodan heat pump. - YouTube

Do you know what flow temperature your system was designed to require at the minimum outside design temperature? Many systems seem to be designed to work at around 45C when it’s around -3C outside, though the lower the better of course with heat pumps.

Do you have radiators in the house as well as the underfloor?

Does the underfloor have a mixing valve? if it does do you know what setting it is on? it might be worth sharing a picture of your manifold if you dont mind.

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Thanks for the detailed response Trystan - although I think I may be more confused now than when I started…

There are two UFH zones each with thermostats, one for the bathroom and one for everywhere else. The advantage of the Salus control for the bathroom is that I can independently warm the floor regardless of the air temperature.

I can control the ecodan via the Mel cloud app but of course with the controller in the loft, its temperature sensor is also in the loft. I don’t know what effect that will have on the efficiency of the system.

Basically, I don’t really understand the difference between the heatpump thermostat and the UFH thermostats. When I request a target temperature for a UFH zone - what is it asking the heat pump to do? And what effect does the Heatpump’s thermostat have?

no idea!

No. There are two floors, and it’s a small house. UFH heats the lower floor, and it’s enough for the whole house with a noticeable but fairly comfortable reduction in temperature on the upper floor.

Yes. Photos attached.

Thanks. Typically with your setup the installer should have configured the ecodan controller for weather compensation mode (this effectively disables the thermostat in the indoor controller which in your case is in the loft).

Weather compensation means that your system flow temperature will vary depending on the outside temperature. So as an example, the flow temperature might be 45C when it’s -3C outside and 35C when its 8C outside.

Technically if that’s setup correctly you could set your zone thermostats to 25C so that they are always on and the system would just run to keep your house at around 20C. If with the zone thermostats are up at 25C and your indoor temperature keeps climbing - this means that your weather compensation curve is set too hot or your controller is perhaps trying to run hot in order to heat an un-heatable loft…

Out of interest, did your installer go through any of this during commissioning? Are you able to get them round to check the settings on the system?

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If your keen to dig into this yourself, it’s worth having a look through some of the Ecodan controller youtube video’s for an overview of how the controller works, it’s all covered in the installation and setup manual as well.

Do you have the original quote from the installer with design details? Did they handle the design and installation of the underfloor as well or was that done by a seperate contractor?

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Any chance for zoomed in pictures of these, when the system is definetly running and the manifold feels warm, cheers!

No, it was quite complicated because it was a complete renovation involving solid wall and floor insulation in addition to UFH. The UFH was handled separately and was installed before the details of the heatpump installation were known.

Ideally I’d prefer to be able to use the Salus controls as these are zigbee enabled and I can integrate them with Home Assistant - one thing I’ll probably want to be able to do is have a lower temperature during the night so it’s easier to sleep.

Thanks for the pointers, and I’ll have a look at the videos and try and get my head round the weather compensation feature.

What temperature are you running the UFH at (from the manifold guages)?

This temperature is controlled by the blending valve underneath the pump. Personally, my UFH runs at about 28°C.

Are both the zones fed by that one manifold (so the actuators control the zones).

Yes but if that is a very low demand on the HP it will cycle and be very inefficient.

We will need some more info on the HP, tanks, buffer tank etc. If you have any diagrams from the installer, that will help.

How long has it been running?

@TrystanLea It was actually set in Weather Compensation mode, but the MEL cloud app was displaying something different. I am not sure if using the app overrides the local controller? Something else I need to investigate.

The initial settings were Flow temp [email protected] deg and [email protected] deg.

I have set it to Flow temp [email protected] deg and [email protected] deg. I have set the UFH thermostats to 25 deg. I will leave it like this for 24 hours and report back - unless it becomes intolerably warm!

One further question though - how do I reduce the temperature overnight - use the UFH thermostats?


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Great, that’s a good starting point, it would be worthwhile checking for system cycling as you reduce the flow temperature. Are you monitoring electricity consumption, logging to emoncms or home assistant?

It is possible to nudge the curve ±a few degrees on the main controller but im not sure if that’s automatable. Several folk here are automating control via melcloud so may be able to advise further @MyForest @Timbones any ideas?

It’s worth checking the setting on that blending valve, you really want that to be set to max so as to minimise blending, you want to have your heat pump reduce the water temperature not the blending valve.

Yes but if it is feeding the UFH directly, 40°C flow temp is possibly far too hot.

However, it does actually depend on floor covering and if the UFH is in concrete or not.

Yes I can monitor consumption using emoncms, I don’t have specific monitoring for the heatpump yet but it consumes the bulk of energy so I can get a rough idea.

The blending valve is at max (I do recall the installer mentioning this).

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The UFH is in screed, which is covered in tile in the bathroom and hardwood in the remainder of the floor.

Initially the bathroom stat was set at max, the idea being I assume to ensure the floor stayed warm regardless of the air temp. I expect this was what was responsible for the initial high energy usage.

Great, good to hear! I’ve seen some heat pump systems with 55C getting blended down…

I’m sorry, I’ve not seen a way to automate altering the weather compensation curve, I re-implemented the logic in my code and then enhanced it. As a result I just keep setting the target flow every two minutes from my code.


Yes that makes sense (code I understand… heating systems are a complete mystery to me). I can set up an automation in HA to do this.

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I saw your other post about just turning the ASHP off during the night (or maybe putting it in ‘holiday mode’). A far simpler solution that I might try before coding something in HA.


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Can you program UFH thermostats with a -2 degree setback overnight? That’s probably your best option.

Ecodan does not provide a setback feature that I know of. Can only prohibit the heating mode for a set time period, which isn’t quite ideal.