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MELcloud scheduling misbehaviour

downfield · 2025-12-02T16:31:25Z

I am aware that there are other threads discussing the shortcomings/confusion caused by the ability to set time schedules on both the Ecodan FTC wall box and the MELcloud app, but I think this warrants a separate thread. I use MELcloud to set the following winter time schedule, viz: 0500 - 2200: 21C 2200 - 0500: 17C. Pretty simple you would think. About 98% of the time it works fine. But seemingly at random it fails either to set back the temperatiure in the evening or to advance it in the early morning. About 5 days ago we realised the house was too warm and it had stayed at 21C all night. This morning I woke at 0700 and realised the house was cold - still set at 17C. Has anyone else seen this behaviour? For the avoidance of doubt, I never use the FTC wallbox to control the schedule, but I do wonder if a setting there is interfering with the MELcloud schedule in some way.

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Air Source Heat Pumps (ASHPs)

Last Post by Abernyte 4 months ago

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downfield

(@downfield)

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Joined: 1 year ago

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Topic starter 12/12/2025 9:52 pm

@davidalgarve I didn't stay on AA for long because it seemed to do a worse job of getting the house to the desired temperature. However I have reconfigured my buffer into a volumiser recently (like you) so perhaps I should give it another try.

I don't really understand what AA is doing though.

MELpump tells me I am getting a COP of 5.1 with an OAT of 8.8C. This drops to a COP of 3.7 with an OAT of 3C.

Mitsubishi Zubadan 14kW with Mixergy 210l DHW in 220m2 barn property. 24 solar panels = 9kWp with GivEnergy 5.0kW Hybrid inverter and 19kWh GivE batteries. Jaga Strada fan-assisted rads throughout. Landvac vacuum glazing/triple glazed windows.

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Abernyte

(@abernyte)

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Joined: 3 years ago

Posts: 260

13/12/2025 11:35 am

Anecdotally, it appears to "learn" how the house cools and heats and then anticipates changes that would effect the IAT. I have noticed over the years that the system compensates for a rapidly falling OAT with bringing the house temp up a bit or conversely stays off. It probably helps that my house is some what leaky and exposed so cooling due to wind wash in the structure is a thing. Not very scientific I am afraid but it feels right!

AA was switched on by the installer, very experienced, who was a fan and the subsequent Mitsubishi service engineers since 2019 have all advocated its use.

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DavidAlgarve

(@davidalgarve)

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13/12/2025 12:03 pm

@abernyte Thanks for your comments. My experience is mainly on weather compensation and latterly on a Melcloud trial which, I believe, uses AA in a modified form.

What seems strange is that throughout my trial period, I have never achieved the set temperature and have always needed to set this higher to achieve comfort level. Is this your experience?

I ask because I will shortly revert to either weather compensation or AA, without Melcloud and would like to know what to expect.

According to MelPump my house has good insulation so this may have to be taken into consideration

342sq m "Upside down" house in Algarve. Portugal
Mitsubishi PUHZ-120YUK 12kW ASHP
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Abernyte

(@abernyte)

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13/12/2025 12:22 pm

No, it gets to set temperature easily even during periods of extreme cold, minus 7C/8C or below. When the OAT drops like a stone it can slightly over compensate by overshooting by a degree on the set temperature.

I have 13 K2 and K3 rads so ample system volume, no buffer or volumiser and single zone, all trv's left open wide so as simple and straightforward as I can make it. I can honestly say it is the closest heating system that I have ever had to fit and forget. It follows the Melcloud set schedules and just keeps the house evenly warm all year.

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