replying to Mike Humphrey, GeoffB wrote:
PS I have studied your reply and thought about it some more. I would like to
add the following note: let's assume that the grey wire from the HW zone valve
is connected to the brown wire, but before the thermostat. So in the case you
describe, the brown wire from the timer to the thermostat would be live, I
agree. But not the wire from the thermostat to the HW zone valve, because the
thermostat switch is open.
The more I think about this, the more befuddled I become.

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