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Mitsubishi Ecodan Fails to Heat Water despite temperature drop

 
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Air Source Heat Pumps (ASHPs)
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Morgan
 Morgan
(@morgan)
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Joined: 4 years ago
Posts: 616
25/06/2025 7:56 am  

@m1kegibson 

This will show you how to check and adjust DHW settings.  He waffles a bit to about half way through then gets to the important bit so far as you are concerned.  Hope this helps.

 

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

2 ESS Smile G3 10.1 batteries.
ESS Smile G3 5kw inverter.


   
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 m1kegibson
(@m1kegibson)
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Posts: 8
Topic starter 25/06/2025 8:32 am  

The settings for DHW are the defaults with the target set to 50 and drop set to 10. The issue is that even when the water temp drops well below 40 it still does not kick in and start heating the water. My daughter is now trained to hit the Heat Now button on the MELcloud app after her morning shower until we figure out why this is happening. 


   
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 JamesPa
(@jamespa)
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Posts: 2580
25/06/2025 10:27 am  

Posted by: @m1kegibson
↑

The settings for DHW are the defaults with the target set to 50 and drop set to 10. The issue is that even when the water temp drops well below 40 it still does not kick in and start heating the water. My daughter is now trained to hit the Heat Now button on the MELcloud app after her morning shower until we figure out why this is happening. 

What's the 40C shown on the display?

It might be worth changing settings and changing them back, it feels like something might be out of sync between ftc and odu, or as @ashp-bobba suggests, calling mitsubishi.

 

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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 Gary
(@gary)
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Posts: 350
25/06/2025 12:17 pm  

@m1kegibson Apologies if I'm teaching grandma to suck eggs but have you confirmed the max temp drop in the controller is set to 10C?  To do that you hold down the menu button for a few seconds till the hot water/heating menu appears then under the tap symbol press the pen/notepad symbol then there you will see the options for the max temp set that should be 50, as that is what Melcloud is reporting, rhe max temp drop value, which you should check is set to 10C.  Then there is the max operation time that will stop hot water cycles if reached regardless of the set temp so check that is set to a couple of hours.  Lastly, there is the time limit that prevents it restarting even if its demanding heat but that shouldn't be an issue at this time of year.

If you are happy to post screen shots of those values then at least we can confirm its all set correctly.

I don't believe its a scheduling issue as your screen shot shows a paused symbol by the hot water symbol and nothing else if it was on a schedule there would be a clock and if it was disabled completely there would be a stop sign so I do believe you are in constant hot water heating mode the unit just believes the temperature is satisified.


   
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 m1kegibson
(@m1kegibson)
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Topic starter 25/06/2025 1:37 pm  

Hep. Max drop is 10C. Tried changing and it 5C made no difference. As you say, DHW set to Constant, target is 50C with 10C max drop. I think I will try setting a schedule and switching to timed operation when next round at her flat to see if that makes any difference. She is waiting for another engineer visit but all they do is turn it off and on and then say “there, it’s working now”!


   
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 JamesPa
(@jamespa)
Illustrious Member Moderator
Joined: 2 years ago
Posts: 2580
25/06/2025 4:32 pm  

@m1kegibson did you try calling Mitsubishi as suggested by @ashp-bobba, it may be the easiest fix!

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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 m1kegibson
(@m1kegibson)
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Posts: 8
Topic starter 25/06/2025 6:28 pm  

Not yet. I am away at present so will do so when I am in front of the controller. 


   
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 Gary
(@gary)
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Joined: 2 years ago
Posts: 350
25/06/2025 8:34 pm  

Posted by: @jamespa
↑

What's the 40C shown on the display?

Its the flow temperature for the heating circuit, it means its running a fixed flow temp and is not on weather compensation, get that changed come the heating season especially with UFH its way too high for all but the depths of winter and in a flat may not even need to get that high


   
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