Roger Mills wrote:

On 03/01/2019 17:50, Mark wrote:
"Roger wrote in message
...

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.


Why are they designed that way ? and not spring loaded back to the Heating
position
if the sync motor fails at least you would have a warm house

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History, probably. They are a development of the earlier diverter valve
- which was either HW or CH but not both at the same time. These always
defaulted to the HW position, and you didn't get any CH until the HW
demand was satisfied.

I suppose it makes sense in that you generally want HW all year round
but only want CH when it's cold. If the valve failed in the summer, you
wouldn't want CH but no HW.

Hmm what would pee you off more
-5c outside and snowed in with hot water but no heating
or 25c outside with no hot water but CH working

-