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Adavison
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October 6, 2025
Solved

Mitsubishi Ecodan: hot water coming on outside of schedule (not due to reheat or legionnaires settings)

  • October 6, 2025
  • 18 replies
  • 1460 views

I recently switched to a cheaper nighttime tariff and want to set my hot water to come on mainly during the night, with a short boost in the early evening. I've set the DHW schedule for the right times but for some reason it still comes on outside of the schedule before the maximum temp drop should kick in. The tank temp is set to 50° with a reheat drop of 15° and this morning is was heating when the tank temp was at 44°. It also wasn't anything to do with the legionaries setting as this had only been run a few days ago.

I have the MELCloud app setup with a schedule for the heating and have tried switching this off to only rely on the control unit schedule and this doesn't seem to help either.

I've attached a screen shot of my last 24hrs temp history which shows yesterday evenings temp boost and since then it hasn't dropped below the 35° that should start the reheat cycle, so as far as I can tell it shouldn't have been coming on this morning.

Does anyone know why this might be happening?

Thanks

Best answer by Ecodanwarrior

Updated on 16/10/25 by Ben_OVO

Ecodanwarrior has posted the following tips for this issue:

 

In the control unit if you click on the button on the far right and then if on the far left the DHW symbol with the thermometer shows its on this could be the reason its heating even before the temp has dropped below the 15 degree limit. I use the thermostats to control when the heating comes on and off not the control unit. The control unit I use to set the temp in the rads. I have our DHW timed on the control unit to come on for a small while in the evening and then for a few hours in the morning, it doesn’t run outside of that.  I don’t have the app so not sure if shutting down the system resets anything when it boots back up

​@Adavison did you check that the two DHW schedules on the control unit are set the same?  I can’t remember off the top of my head how it works but I think you can set the DHW for different times of the year.  I think I just setup the two identical, could be that the timer on the control unit is following a schedule where for the month of October the DHW is off

18 replies

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Chris_OVO
Community Manager
Chris_OVO
Community Manager
October 10, 2025

Hey ​@Adavison,

 

I'm so glad to see you and ​@Ecodanwarrior teaming up on this! It would be fantastic if you could keep us in the loop about your progress. It could really help others in a similar situation. Keep up the great work!​

Renewable energy jokes never get old.
    A
    Rank 2
    AdavisonAuthor
    Rank 2
    October 10, 2025

    ​@Chris_OVO, I’m testing now so will update with what I find 👍🏼

      Ben_OVO
      Community Manager
      Ben_OVO
      Community Manager
      October 13, 2025

      Thanks ​@Adavison, and many thanks ​@Ecodanwarrior for your great help here - very much appreciated!

       

      ​@Adavison we look forward to hearing how it goes.

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        AdavisonAuthor
        Rank 2
        October 13, 2025

        ​@Ben_OVO not well is the answer, sadly.

        I've switched off the app schedule and reset the controller schedule, but that doesn't seem to work at all and neither is the reheat setting kicking in without manual intervention.

        As an example, I have the heating set to come on at 6pm in the evening to make sure there is enough hot water for the bath. The max temp. is set to 50° with the reheat drop setting at 10°. Last night the tank temp was showing at 16° but at 6pm the heating didn't come on until I switched it to prohibit and then back to schedule again.

        The same thing happened later that night when it was supposed to come on at 11.30 and I had to manually intervene again.

        I've tried resetting the schedule a couple of times and switching the unit off at the mains as suggested online, but still no joy.

        I'm guessing this must be a software issue but thought I'd check in one last time to see if anyone had another idea before I call out an engineer.

        Thanks

        Ben_OVO
        Community Manager
        Ben_OVO
        Community Manager
        October 14, 2025

        Ah I’m sorry to hear that ​@Adavison, I really hope you can get to the bottom of this soon.

         

        Unfortunately my knowledge of heat pumps is very limited, so I’m hoping ​@Ecodanwarrior might have some further wisdom to share. It’d be great if this could be solved without a callout. There’s some info in this previous thread which you might find useful too:

         

         

        I’ve also found this Renewable Heating Hub forum which may be of help.

         

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        EcodanwarriorSolved
        Rank 2
        October 14, 2025

        Updated on 16/10/25 by Ben_OVO

        Ecodanwarrior has posted the following tips for this issue:

         

        In the control unit if you click on the button on the far right and then if on the far left the DHW symbol with the thermometer shows its on this could be the reason its heating even before the temp has dropped below the 15 degree limit. I use the thermostats to control when the heating comes on and off not the control unit. The control unit I use to set the temp in the rads. I have our DHW timed on the control unit to come on for a small while in the evening and then for a few hours in the morning, it doesn’t run outside of that.  I don’t have the app so not sure if shutting down the system resets anything when it boots back up

        ​@Adavison did you check that the two DHW schedules on the control unit are set the same?  I can’t remember off the top of my head how it works but I think you can set the DHW for different times of the year.  I think I just setup the two identical, could be that the timer on the control unit is following a schedule where for the month of October the DHW is off

          A
          Rank 2
          AdavisonAuthor
          Rank 2
          October 14, 2025

          ​@Ecodanwarrior you're a legend! I hadn't spotted the double timers and they were of course clashing, so I've just switched the other one off and looks like it's working ok now. Thanks for yours and ​@Ben_OVO's help!

            Ben_OVO
            Community Manager
            Ben_OVO
            Community Manager
            October 15, 2025

            Morning ​@Adavison and ​@Ecodanwarrior,

             

            ​@Ecodanwarrior thank you so much for your help here, we’re lucky to have you on this Forum! I’m really happy it’s working for you now ​@Adavison, and let us know if you ever have any other questions!

             

            Cheers both.

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