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

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)


Yes that's right.
When a bi-metal strip type room thermostat closes it applies mains
voltage across a small resister in close proximity to the strip.
Its called the pre-heater.
The idea is to make the thermostat switch off a little earlier than
it would otherwise do.
In technical terms it reduces the hysteresis of the feedback system.
http://en.wikipedia.org/wiki/Hysteresis
As there is no neutral to complete the circuit it doesn't work.

My advice is dump it and go digital.
--

Graham.
%Profound_observation%

When I say a small resistor I mean a physically small high resistence.
About 220K-ohms IIRC
--

Graham.
%Profound_observation%

Graham wrote:
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)


Yes that's right.
When a bi-metal strip type room thermostat closes it applies mains
voltage across a small resister in close proximity to the strip.
Its called the pre-heater.
The idea is to make the thermostat switch off a little earlier than
it would otherwise do.
In technical terms it reduces the hysteresis of the feedback system.
http://en.wikipedia.org/wiki/Hysteresis
As there is no neutral to complete the circuit it doesn't work.

My advice is dump it and go digital.

Having fitted a digitstat, and having loads of mechanical stats as well,
I have to agree whole heartedly. A program of replacMEnt as time and
money allows will happen, honest :-)

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
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!

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
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!

Thanks for advice guys.
Al