Posted by: @derek-m

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Is the timer cheaper than a contactor?

Possibly. It's quite a long run from the outside box to the DHW tank immersion heater, cable don't come cheap these days. The timer is very basic.

I also like the fact it is totally separate, because I have an alternative I can use for DHW if the heat pump goes on the blink.

I think there might also be ampacity problems if the actual current used to heat the immersion heater came from the PCB, so some sort of local to the tank AC relay might be needed. 

@derek-m thank you. I’m going to stick with setting it manually to the temps as you suggest- 42 at -10 (as it did get that cold in December!) and 25 at outside of 20 and see how I go. 
I may then have a play and see what the high low settings do!

Posted by: @cathoderay

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Posted by: @derek-m

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Is the timer cheaper than a contactor?

Possibly. It's quite a long run from the outside box to the DHW tank immersion heater, cable don't come cheap these days. The timer is very basic.

I also like the fact it is totally separate, because I have an alternative I can use for DHW if the heat pump goes on the blink.

I think there might also be ampacity problems if the actual current used to heat the immersion heater came from the PCB, so some sort of local to the tank AC relay might be needed. 

That is the reason for the contactor, a signal cable from the heat pump controller operates the contactor, this in turn connects the higher current electrical supply to the immersion heater. 

@cathodeRay @Derek-M - I know that the immersion is wired completely separately. On the all for DHW water I ahead not tried the 2 options- ‘turn in TBH’ or ‘fast DHW’, will give them a go at some point and see if anything happens!

@curlykatie - I think the setup we have, separate and independent wiring for the immersion heater, with no connection to the heat pump controls, is the standard set up, at least if Freedom were involved, as in supplied the heat pumps and instruction on how to install it. See the earlier images I posed from the installation manual. As I said earlier, I like this set up, it is simpler, and it also provides a back for hot water if the heat pump packs up.

I'm still sorting out the aftermath of Saturday's heat pump delinquency. Before Saturday, I had the heat pump DHW on a schedule in the wired controller, timed to come on between 1300 and 1400 only (in a bid to use the warmer part of the day for the hot water heating) and it worked. The DHW On/Off (squiggles on/off by the right hand tap symbol) worked as it used to, as a mains level on/off, like turning an immersion heater on/off at the wall/mains. Whether the actual heating element was heating was determined by a combination of the timer and the hot water temp, meaning it only came on (a) if the water was below 40 degrees (I have a DHW set temp of 50 degrees, and you can set the 'delta T' for the number of degrees below the set temp the water needs to get to for the hot water heating to come on in the For Serviceman settings (DHW Mode Setting 1.6, dT5_ON); I have mine set to 10 degrees so it comes on at 40 degrees) and (b) the time is between 1300 and 1400 hours. At the moment, the DHW On/Off on the front page turns the hot water heating on even when outside the temp and time limits eg 1800 yesterday, DHW tank temp 41, so should not call for heat, but it did. Grrr. It's a good thing I don't have a revolver in the house, because if I did, there wouldn't be much of that wired controller left by now.

Part of the reason for this long account is I said elsewhere and perhaps here the DHW front page On/Off is only in the sense of 'on/off at the mains', not actually turning on active hot water heating. Now it seems it can be either...     

@cathoderay sorry you are Having so much trouble… it’s really not very user friendly at all, and often has a mind of its own!! I have the DHW set to 50 (and to re-heat after a 10degree drop), at the moment to come on twice a day. We are having issues with th whit water temp fluctuating upstairs still, but once this is sorted I may reduce to once a day heating… 

moor immersion just has an on/switch, which I have asked for a timer to be fitted to the legionnaires.. I am not very good at remembering to do it manually!

@curlykatie - I'll probably get taken out side and shot for saying this, but you might want to google whether you really need to do the Legionella thing. In my opinion, the risk of Legionella's in a closed domestic hot water system in regular use is very low. Just think of the old days, when we had semi open water storage tanks in the attic, and how many people got Legionella's then!

@cathoderay yes- I’ve been reading mixed advice online… I’ll probably push to get the timer fitted anyway, and then I can decide whether to use it or not!!

What app are you referencing in the comments? I have been looking for one for ages as my Midea control is not really accessible.

@paul436 it’s called MSmartHome in the App Store…

@curlykatie Hi there, thanks for the information in this thread, I am 2 years into my Midea "journey" and it really is like the dark arts, sadly I also had a fit and forget installer so no help there.

@curlykatie it's been over a year now. Did you manage to figure everything out and how's the system performing?