Roger Mills wrote:
In an earlier contribution to this discussion,
Al M wrote:

My house was built 2002 with an oil fired boiler and has two heating
zones, one upstairs and one downstairs with a wall mounted thermostat
(in bedroom and livingroom) for each zone . There are no TRVs
anywhere. (I'm using a digital 3 channel programmer to time the 2
zones and the hot water.)
Problem:
The thermostats work if I manually turn them up and down but they
don't seem sensitive enough to adjust with the rise and fall in
temperature. What I mean is if the temp is high and the heating on I
turn the dial down until it just clicks off. (say 21deg) Next morning
when its freezing cold the heating hasn't come on.
My thoughts are that it's because the stats only have two wires going
to them so the stat is only switching the live feed to the motorised
valve. There is no neutral wire to actually make the thermostat itself
work "properly". (not sure how to explain this technically)
Would a digital thermostat with a battery power source solve my
problem or am I missing the point?
I don't want to have to start tracking wall and rewiring.
Any advice?
thanks

AL

It sounds as if your stats have a *lot* of hysteresis - assuming that the
timer for that zone is actually on, and that the volt-free contacts on the
zone valves are wired correctly.

A mechanical stat with an accelerator heater built in - requiring a neutral
connection - would probably improve matters. But as others have said, a
digital stat would be far better and would provide much closer temperature
control without requiring any additional wires. If you go down that route,
you can automatically programme different temperatures at different times of
day if you wish, as well as getting a free frost stat. You'll need, of
course, to set the 3-channel programmer to 'constant' for any zones
controlled by digital programmable stats.

I would be inclined to fit digital programmable stats on both heating zones,
keeping the existing cylinder stat which will continue to be controlled by
the appropriate channel of the 3-channel timer.
--
Cheers,
Roger
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Thanks for advice guys.
Al