Viessmann 200w with LLH & heatmiser multi zoned UFH

[tonysss13]

I have had a Viessmann 200w since around 2017. It was originally installed with weather compensation to our existing rads with mixed success, the installer who was Viessmann trained did a disapearing act soon after. Since then we have had a full refurb and installed UFH throughout with 4 manifolds for the different areas, and one Radiator in one of the living rooms (which also has UFH). It has been somewhat cobbled together bu different plumbers with differing ideas as the project went on

These all fire the boiler via external demand, and there is a sensor in the LLH.

I have fixed some clip on thermostats to the flow to the LLH, the outlet of the LLH & the return to the boiler. The outlet of the LLH struggles to get above 40c and the linet only reads 50c despite having the external demand set at 70c. Am i I right in thinking the boiler should be attempting to heat the LLH sensor to 70c?

I appreciate 70c would be too high however 40c is strugling to overcome the heatloss in one of our bedrooms when temps outside are below zero.

I am also wondering whether this set up is the most efficient. I have read that rather than using external demand I can use the thermostats to open zone valves & trigger UFH pumps & the pump immediately after the LLH , but dont wire into external demand but use weather compensation to detect demand from the LLH sensor?


thanks in advance