thescruff wrote on May 31st, 2015, 7:08pm:would still like to know what room stats you have/intend to use.
What you have to remember is you'll be powering the brown (MV) from 2 different sources, and can be highly dangerous to anyone working on the heating in the future unless you can include a common isolator.
One of the room stats will be either...
http://www.ebay.co.uk/itm/Digital-Under-floor-Heating-Programmable-Thermostat-Ro...or...
http://www.ebay.co.uk/itm/Digital-Underfloor-Heating-Programmable-Thermostat-Roo...The other stat may be the same as above but, initially, I'll probably use the existing Landis & Gyr Chronogyr REV10 (an old (mid 90s) digital thermostat that still works) to test the idea and its usefulness.
http://www.forum-chauffage.com/images/thermostat-landis-gyr.jpgInterestingly, the Landis & Gyr stat partially does what I'm trying to achieve as you'll see from the image but I haven't been able to find a modern stat that does the same thing, which is the reason for my proposed solution.
The thermostats will be located near each other with common connections made locally so the MV will only see one source. I'm aware that this arrangement will be unusual so I shall be very careful to avoid leaving nasty surprises for others who may work on the system!
Lectrician wrote on Jun 1st, 2015, 6:18am:Live from programmer into both stats. Output from one stat to L1 of switch, output from the other to L2. COM to the brown of zone valve.
It will do what you want, but not very conventional.
There will only ever be one stat feeding the zone valve.
This appears similar to my proposal but with the two way switch after the stats instead of before them. I'd be interested to know why you think that would be a better arrangement. It's good to know that you think it will work OK so I just need to try it.
Although this arrangement is not very conventional, it is innovational and could become conventional if enough others needed to achieve the same result. A better solution would be for thermostat manufacturers to include the features I'm seeking in their products, similar to those incorporated by Landis & Gyr in the mid 90s (see above). There may be some on the market of course, but I don't know of an easy way to find them.
Thanks for your help.