There is a way around it.

Use a Danfoss RF cylinder stat and 2 Danfoss RX1 receivers (one at the
boiler and one at the valve)

When the Stat swichs both RX1 receive the signal and control the boiler and
valve seperatly but at the same time.





"Set Square" wrote in message
...
In an earlier contribution to this discussion,
John Cross wrote:

There's no problem in using an RF tank stat - but I haven't come
across any RF zone valves with remote motor controls and volt-free
contacts - which is what you would need to avoid having to run
cables to it.

What about using a RF tank stat, and a seperate wired stat and zone
valve locally on the cylinder.

At the preset temp the wired stat could close the zone valve, and the
RF stat report back to the boiler to switch off.

By using two stats you may have a slight difference in switching
temps (which may cause a little bit of cycling) but it should work ok.


It would get round the wiring problem - but it's a hell of a fudge!

The idea is supposed to be that the stat opens the valve, and that the
volt-free contacts on the valve turn the boiler on when the valve is
open -
thus providing a sort-of closed loop control system. What you're
suggesting
would be open loop. If the two stats switched at different temperatures
(which they inevitably would) you'd either have the boiler running with
the
valve closed (may not matter on a gravity system) or you'd have the valve
opening but no boiler action (unless the boiler was on for the benefit of
the CH).

In fact, it probably *would* work - but try explaining it to anyone
needing
to work on the system!