On 01/01/2019 12:07, David wrote:
snip

Oh, and thank you for your comprehensive explanation; just one thing,
though; I thought when there was no call for HW or CH the valve,
unpowered,
returned to the mid position. To go HW only or CH only required power to
move the valve to close off the other feed. But I may well be wrong.

Oops!

"The valve has 3 pipe connections, in a T formation. The centre leg of the
T is the inlet and the two short arms are the outlets, usually referred to
as ports A and B. Actuation controls whether the flow from the inlet
passes to the A or B port. In the resting state flow is to the B port
(usually the hot water circuit)."


Cheers


Dave R



Correct. Although, when both demands are removed (but HW-off is still
live) the valve tends to stay in the position it was last in until a new
demand appears. That's why you have to remove ALL power in order to
re-boot it - so that it doesn't even have a HW-off signal. When you
remove the power, you can often hear it whirring back to the HW position.
--
Cheers,
Roger
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