Thanks for the replies everyone. Some good intel I here. Unfortunately for me I'm still no further ahead. Have had a bit of back and forth with Honeywell tech support, nothing glaringly wrong on the install side yet.....
My issue is if I was to upgrade to HR92s then I'm likely stuck with 10 HR91s that are of no use to me and which Im unlikely to be able to return (been unboxed/fitted etc). So £££££.
My other get out is new valves. Again. The danfoss ones were fitted for this purpose, so it won't come cheap, but it would be cheaper than HR92s. If this does come about - what valves are 100% compatible with HR91s so I can guarantee I won't hit the same issue again? Honeywell Valencia's?
https://www.screwfix.com/p/honeywell...questid=353169
Many thanks for your wisdom!