Subsequent to writing the above one more niggle occurred to me.  Whilst you set up the upstairs you need to ensure that the heat pump isnt disabled because the heatmiser isn't 'calling for heat'.  This is of course an undesirable consequence of multiple control systems - they fight both you and each other.  There needs to be one boss!. 

I presume that the 'boiler' light on the heatmiser indicates whether it is calling for heat or not, and I also presume that it does so if any one zone 'under its control' calls for heat.  What we dont know is whether its connected up to the ecodan and how.  Hopefully the heatmiser and the upstairs thermostats are wired in parallel (logical OR), so that if any one is 'on' the heat pump is 'on'.  Or alternatively the heatmiser call for heat may just switch one of the pumps so that its not connected to the ecodan at all (if you follow the wiring you may be able to work that out).  On the other hand....

The only way to find this out is either to inspect the wiring or play with the thermostats.  If its not immediately obvious from the wiring I would suggest to start the procedure by turning down all the heatmiser thermostats until the Boiler light goes off.  Then turn up the upstairs thermostats.  If the heat pump comes/stays on they are in parallel. and you are good to go.  If the heat pump stays off then we have a problem and we need either bypass the heatmiser or arrange that its permanently calling.  The latter is probably most easily done by whacking one of the heatmiser thermostats up to max, so the zone never reaches temperature.  

Let me know what you find and I may be able to come up with other suggestions.  As I say heating systems need exactly one boss!  Unfortunately UFH design is often done separately to whole system design (and whole system design is often poorly done) which unnecessarily complicates matters.

PPS Just checked the heatmiser manual  The call for heat to the boiler from the heatmiser is just a volt free contact (which is what the Ecodan will have).  So simply connecting the wires that go to LS and LR together is a backstop to ensure constant call for heat if the above doesn't work!

+1 from me on @jamespa's advice.

From what it seems to me, you have a setup that is, apart from a few extra gadgets that would be best removed, exactly what most of us would want to aim for, so the problem for you is one of configuration. This, if we're right, is good news since the only cost is a bit of time and perhaps a few days of slightly compromised comfort whilst the trial and error goes on.

With regard to the running costs, one thing that hasn't been said - albeit hinted at - is that getting a heat pump, especially with solar PV and a battery, can significantly reduce costs but will also polarise those costs greatly. For instance, last January I exported almost nothing, the heat pump was going great guns and the EV was less efficient because of the cold so my net consumption for that one month was 24.43% of the annual total. The four cold months (Jan, Feb, Nov, Dec) accounted for 76.26% of the annual total - three quarters of the consumption in one third of the year. That's pretty scary when you're in the middle of it because it's natural to assume things stay pretty constant, but, as @jamespa said, things do balance out; May and June were months where we generated more than we used, even after taking the EV's voracious appetite into account.

Posted by: @majordennisbloodnok

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+1 from me on @jamespa's advice.

From what it seems to me, you have a setup that is, apart from a few extra gadgets that would be best removed, exactly what most of us would want to aim for, so the problem for you is one of configuration. This, if we're right, is good news since the only cost is a bit of time and perhaps a few days of slightly compromised comfort whilst the trial and error goes on.

With regard to the running costs, one thing that hasn't been said - albeit hinted at - is that getting a heat pump, especially with solar PV and a battery, can significantly reduce costs but will also polarise those costs greatly. For instance, last January I exported almost nothing, the heat pump was going great guns and the EV was less efficient because of the cold so my net consumption for that one month was 24.43% of the annual total. The four cold months (Jan, Feb, Nov, Dec) accounted for 76.26% of the annual total - three quarters of the consumption in one third of the year. That's pretty scary when you're in the middle of it because it's natural to assume things stay pretty constant, but, as @jamespa said, things do balance out; May and June were months where we generated more than we used, even after taking the EV's voracious appetite into account.

Worth also adding that, assuming you know the rough overall annual costs, then most, if not all, energy suppliers will enable you to pay via a fixed monthly direct debit, which will enable you to even out the cost over the year, if you prefer this to incurring it in real-time.  I use my Octopus account in this way, allowing it to build credit in the summer and then letting this get utilised in the winter.

Posted by: @majordennisbloodnok

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Marvellous. And what tariff are you on with which supplier?

We're looking to go with Octopus, but waiting for the solar guys to talk us through everything. 

Thanks, as always, @jamespa for your help and advice here. This sounds like a sensible way forward. The installer got in touch with us today and he will be coming round tomorrow, so I am going to scour your posts to come up with a list of questions for him. I think one of the major ones is understanding what all those pumps do and how the UFH and rads relate to one another. I don't know if it's possible, but I'm keen to understand whether it's possible to get another Mitsubishi wireless RC for downstairs and run the UFH off that. However, as it's all Heatmiser, I wonder if we're just a bit stuck with what we've got.

A couple of questions based on your very helpful way forward

Posted by: @jamespa

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Turn off all room influence on the mitsubishi controller, operate on pure WC

So, all thermostats on MAX, open or remove rad TRVs, and adjust the heating schedule to run permanently at 21c (rather than scheduling set-backs) for the time being?

Posted by: @jamespa

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If you are heating your DHW to more than about 48 you are wasting energy. 

Heating is set to 48c, but we'll experiment with moving that down a touch.

Posted by: @jamespa

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PPS Just checked the heatmiser manual  The call for heat to the boiler from the heatmiser is just a volt free contact (which is what the Ecodan will have).  So simply connecting the wires that go to LS and LR together is a backstop to ensure constant call for heat if the above doesn't work!

 

A question I'll definitely be asking of the installer. Thanks so much to all of you for your support. Communities like this are a real godsend. I'll let you know how I get on tomorrow!

GF

Posted by: @green_fox

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I'm keen to understand whether it's possible to get another Mitsubishi wireless RC for downstairs and run the UFH off that

Doubtless its possible but Im not currently sure its necessary or even desirable.  You have plenty of kit much of which is unnecessary and unhelpful, before spending money on yet more kit I would seek to get it working in the simplest way possible.  The challenge, quite honestly, is to set it up in a way that disables most of the controls so that there is only one boss, ideally so that it runs purely on weather compensation with any remaining thermostats acting as limiters to deal with solar gain, not as controllers.

Posted by: @green_fox

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So, all thermostats on MAX, open or remove rad TRVs, and adjust the heating schedule to run permanently at 21c (rather than scheduling set-backs) for the time being?

Yes, to get the upstairs at a comfortable temperature and running on WC turned down as low as is consistent with heating the upstairs.  Once thats working satisfactorily you can deal with the downstairs which for the time being can remain on thermostats provided you deal with the 'call for heat' issue mentioned above, if indeed there is one.

Posted by: @green_fox

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I'll let you know how I get on tomorrow!

Good luck.  Depending on the installer they will either be helpful or give you a load of BS and tell you not to touch anything.  If they do the latter, which on balance is probably the more likely, just note what they say and any nuggets of actual information and come back here!  What you could really do with is a system diagram (electrical and plumbing) and almost the best thing the installer could do is provide one.  Its unlikely to happen though, that mess of wires loosely hanging tells you something.

Posted by: @green_fox

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Posted by: @majordennisbloodnok

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Marvellous. And what tariff are you on with which supplier?

We're looking to go with Octopus, but waiting for the solar guys to talk us through everything. 

That makes plenty of sense. Perhaps more importantly, Octopus seem happy to accommodate people changing their minds quite regularly. When I last switched tariffs, they said I'd have to stay on that tariff for at least a month before being able to switch again, which is a far cry from the "at least a year" lock-in I was expecting. As a result, you can pick a tariff that works for you now (e.g. a tariff that gives really cheap night-time rates to fill the battery that you can then use during the peak rate) and then move to another tariff in a few months once you've got a better handle on the nuances and complexities. Remember, also, that you now need to consider import and export tariffs.