OK so you can prioritise hot water with a simple diverter valve but don't jump in with a Heatmiser UH4 set up!
The R. Cott. heating system now works but wasted 2 days of electrician time.
Detail available if anyone interested.
Further question arising from a perceived risk to underfloor pipe work if the mechanical thermal regulator fails.....
The suggestion is to fit an *over temperature* cut out to the manifold pump. Not good for me because the diverter valve circulates water at 70 deg. plus during overrun when the DHW stat opens. My Viessmann boiler offers weather compensation and I am wondering if this can be adapted to give a *set back* output temperature for the underfloor system. Easy with a combi but system boiler...?