UPDATED - 6th May
Still experimenting with settings using MQTT (doesn't seem hopeful ATM, but early days yet!)
MQTT published every minute or when http call makes a 'valid' change to the settings Otherwise no calls seem to work
Temperature can be changed AND Position can be changed (Automatic Temp Control en/dis) (MQTT/HTTTP) (Not yet sure what actual interaction is with TRV, assume stays in set mode (Auto Temp Control) )
Only 2 MQTT messages come back
EDIT & UPDATE - 6th May
Major Observation: Summer is not the time to set about configuring a TRV on a radiator in Node-RED or indeed any other Control System. No heat is required!! 
Played around with everything and ended up with this as the final flow to control the valve. Still need to get the MQTT alive/announce messages monitored. But the TRV is not that easy to switch on and off - needs resetting all the time.
Updated flow using @Colin node-red-contrib-pid. Unfortunately due to my 'Major Observation', I can't set the system up without wasting a lot of heat and sweating my eyeballs out!!
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