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Mitsubishi Ecodan stuck on immersion symbol

ak2024 · 2024-10-11T12:38:28Z

The unit is programmed to start legionella every 2 weeks at midnight, however, for some strange reason it comes on anytime and around 3 or 4 times every 2 weeks. Even stranger is that it doesn't actually heat up the water, you can see over time that the water temperature drops from 49 to 16 Celsius. One time I tested the water temperature with a thermometer, it displayed 17C on the system screen, but the actual water temperature was 46C, however the water temperature does drop over time. The system will be stuck on this mode for around 2 days, and during those 2 day I won't have any heating or hot water. The system doesn't consume any additional electricity during this mode.

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Air Source Heat Pumps (ASHPs)

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Toodles

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05/01/2025 7:42 pm

@ak2024 Our Daikin cycled 10 times in 24 hours at approx. ~-1 deg C. Regards, Toodles.

Toodles, heats his home with cold draughts and cooks food with magnets.

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Gary

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05/01/2025 7:47 pm

They could be defrosts but unlikely at that Frequency.

do you have the MELCloud app that can show the flow and retune temps for those times?

There is an hourly chart that is useful

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ak2024

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Topic starter 05/01/2025 8:12 pm

@gary

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Gary

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05/01/2025 8:23 pm

That’s definitely cycling do you have UFH or rads regardless of which it would suggest you have only a very small proportion of the heating system calling g for heat. Do you have a lot of zoning in the house?

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ak2024

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Topic starter 05/01/2025 8:51 pm

@gary

I have UFH on ground floor and rads on 1st floor. 2 Zones have been setup, ground floor and 1st floor. There are also individual thermostats for UFH in each room.

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Gary

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05/01/2025 9:01 pm

That will be the cause then, with only 1 thermostat calling for heat the water volume is too small it heats quickly and the heat pump has to turn off then back on again when it cools. Ideally you want all circuits calling at the same time. What make of thermostats are the UFH zones on? Do they connect to a wiring centre that turns the actuators on for each circuit? If so you can unscrew the actuators for the UFH loops that will mean they are all open all the time so when one zone calls for heat water will flow round them all. This will mean you have more water volume for the heat pump to react to giving it more chance to find the correct input power before the water over heats

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ak2024

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Topic starter 05/01/2025 9:17 pm

@gary

I have 1 of each of the right Mitsubishi controller, one on the ground floor and one on the 1st floor. The EPH controllers control the actuators. I have a EPH controller in every room, around 5, on the ground floor for the UFH. The Mitsubishi is wireless and the EPH is hardwired.

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Gary

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05/01/2025 9:26 pm

So presumably the EPH thermostats are wired back to a controller near to the UFH manifold? Do you have a picture of that?

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ak2024

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Topic starter 05/01/2025 9:30 pm

@gary That's in an awkward place, hard to get to. The EPH do control the actuators, but the underfloor heating won't come on until the Mitsubishi controller temperate is set above the current room temperature..

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Gary

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05/01/2025 9:42 pm

Yep that all makes sense the easiest solution is to remove all the actuators from the UFH manifold they should just unscrew them all loops will be open when thermostats call for heat.

Or as you need the mitsi thermostat to be calling for heat for the heat pump to fire up. Then just increase the temp on all the 5 zone stats to a high level then the UFH will only come on when the mitsi thermostat calls for heat. Depending how it’s wired then downside of that may be that there is an extra circulation pump for the UFH that will run constantly once you set the zone thermostats to constantly call for heat

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ak2024

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Topic starter 05/01/2025 10:04 pm

@gary The second option would have been great but when the UFH comes on 3 rads on the 1st floor also come on.

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Gary

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05/01/2025 10:09 pm

Ideally you want it all to come on at the same time. When my hall thermostat calls for heat all of the UFH loops downstairs come on and all the rads upstairs come on. Upstairs can be kept cooler than downstairs by turning down the lock shield valves to reduce flow. If you have more water volume you can run at lower flow temps without cycling

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