Mitsubishi Ecodan Fails to Heat Water despite temperature drop

m1kegibson · 2025-06-23T09:41:54Z

My daughter has recently moved into a new flat where water and heating are provided by an Ecodan ASHP. When she moved in I tested the underfloor heating and it all seems to work with the zone valves opening and the ASHP kicking in to circulate water through the manifold/underfloor pipes etc. So far so good. What I did notice however is that the hot water did not kick in despite the water in the tank being more than the configured 10 degrees below target. The Hot Water is set to continuous (not timed). The engineer looked at the system and after turning off/on, the ASHP kicked in and heated the tank water. However, after using hot water and the tank temp again dropping below target, the ASHP did not kick in. The control panel never indicates that the system is demanding the ASHP start up and heat water. Again, if turned off/on, the heating cycle begins, heats the tank but again never replenishes the hot water. The engineer has visited 3 times now and nothing has changed. Does anyone have a clue of what might be happening here?

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Morgan

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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.
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m1kegibson

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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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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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