I'll leave it tonight and post the graph tomorrow to see it anything starts to make sense !

@bontwoody "but after a minute the 3 way valved closed."

I might be wrong but could it be a 3 port, 2 way valve with mid-position?

Operation by the following voltages

My question would be is it a new valve or the original, has it been plumbed correctly, has the wiring to it been disconnected and reconnected correctly?

Was the new tank fully recommissioned and signed off accordingly as per Mixenergy installation manual?  It kind of sounds like to me it hasn't been😗 Is that a fair assessment?

@jamespa @old_scientist

@iaack Hi, thanks for the input.

So the situation is that I had a direct mixergy cylinder fitted 3 years ago but plumbed my heat pump ready so that I could add the Mixergy heat exchanger at a later date. The original cylinder failed and the replacement I was sent is an indirect cylinder.

Getting the plate heat exchanger isnt really financially viable at the moment so I thought I would try partially heating it from the coil.

The plumber who installed the new cylinder wasnt very confident with the wiring around my PV diverter so I said I would commision it as he was nice enough to plumb the coil into my system for me.

I dont think I have a mid port valve (I hope!) as I made that mistake in my last house and knew the issue  Picture of my valve is below.

This mornings DHW run shows the same pattern. The flow rate is shown in red.

I may have found the problem. There is a valve on the return side to stop the water when it was originally plumbed in with nowhere to connect to. It was closed! I've opened it and will try again tonight 😁

Fingers crossed @bontwoody

@old_scientist Well it does seem pretty evident that it wouldnt work with it closed 🙂 but its odd OEM was showing flow, so lets see!

@old_scientist Yip Yip! it worked.

So the DT was small, probably because the stratification pump is off and the coil isnt big, but it got to a 40% charge on its own before it was stopped and the immersion kicked in. COP was pretty dire though averaging about 1.4. Ill try it in eco mode now which should be slower and give the water more time to conduct the heat away.

Posted by: @bontwoody

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So the DT was small, probably because the stratification pump is off and the coil isnt big, but it got to a 40% charge on its own before it was stopped and the immersion kicked in. COP was pretty dire though averaging about 1.4. Ill try it in eco mode now which should be slower and give the water more time to conduct the heat away.

If you can turn on the destrat pump COP should improve because the water in contact with the coil will be colder.  You will also heat more of the tank likely to a higher temp.

@jamespa absolutely. But I think I might have to get the Mixergy Control unit to achieve that. Ill keep my eyes open on ebay. In the mean time I will also drop the desired tank temperature and maybe heat in short batches with a longish gap.

@bontwoody so pleased it's finally working. 

Posted by: @bontwoody

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@old_scientist Well it does seem pretty evident that it wouldnt work with it closed 🙂 but its odd OEM was showing flow, so lets see!

Yes, this is what threw me when I read your post yesterday - how were you recording flow for 1min with a closed valve, and if there were no flow, why did the controller not immediately raise an E911 error code. Anyway, kinda irrelevant now it's working.

I hope you are able to improve the COP a little. I use Quiet Mode to limit the output when heating my DHW, which hopefully makes it a little more efficient (lower and slower). My LWT normally sits around 8C above the DHW tank temp during the DHW heating cycle. Without Quiet mode enabled, it's a little higher.

Don't forget to turn Quiet Mode OFF when going back to space heating as it does strange things in space heating, as noted by Glyn Hudson here

@old_scientist yes. No E911 error. Very odd. Thanks for the link, very interesting.

@old_scientist @jamespa

So this was last nights DHW run using economic mode.

Im a bit unsure as to what the actual COP was as it states 3.00 for the whole window, but the instanteous values are much lower. Either way its better than last night.

Ive knocked the target temperature back 5C and scheduled two 30 minute runs with a break for tonight. 🙂