On 04/03/2021 13:59, Dave Plowman (News) wrote:

He was an expert on Viessmann boiler related stuff. So would likely know
about using a system boiler with a heat store. Even my now quite old
Viessmann can communicate with other devices. So it's possible they do a
pump controller for a heat store. But just musing.



The issue is I can't use an external controller .. I have a full
controller for Underfloor Heating (17 zones) so that needs to stay.
It needs to control the pump .....
Its mains pressure HW through a heat exchanger in the Thermal store ...
once you start running HW after a couple of minutes the water around
heat exchanger will cool
The control start the boiler pump - so it 'stirs' the store without
powering up boiler, meaning you can get loads of DHW before it needs to
start boiler and replenish the Thermal store.
Added advantage is that I have my Solar panels on roof dumping any
excess electricity into the Thermal store .. in Summer boiler never
fires up at all.


I found Tech Help email address for Viessman so will ping them a mail