In an earlier contribution to this discussion,
dennis@home wrote:

But if the system already works like that then its reasonable to
extend it in a similar way.

No it isn't!

The conservatory will get heated to its TRV setting even when *no* heating
is required - as will the room in the house with the room stat - when *only*
the conservatory is required to be heated.

The difference is that when you want to heat the house, you are presumed to
want to heat the
*whole* house (without conservatory) - and the current TRV solution makes a
reasonable job of that. As soon as you introduce another zone which requires
*independent* control, the whole thing falls down unless you zone it
properly.

Simply wiring two stats in parallel *WILL NOT* meet the OP's requirements.
--
Cheers,
Set Square
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