My CH system currently has two 2-port zone valves - made by Satchwell Sunvic.
The motors drive one way to open and the other to close. No power used once in
position. I should like to add a third zone but all the common valves I have
found from my usual suppliers - screwfix/toolstation (Honeywell, Drayton,
Danfoss etc) seem to be the spring back type. Is there a replacement available
of the same type as the Sunvic?

Geo