If you remove the stat and touch the two wires together, does the valve open
and circulator run?. The boiler won't necessarily start as it may already be
at high limit. If things run properly by touching the wires together, and
since you say you've already swapped the thermostat with another, I would be
looking for a weak transformer powering the zone valve(s). There may be one
or several. You need to find them and look for the wattage (VA) Standard
heating transformers are 40 VA, but sometimes zone valves are powered by the
transformer in a switching relay or aquastat relay.
"Achattaway" wrote in message
...
Thanks for the replies so far. I have checked out the following as
suggested: The wiring instructions for the thermostat do not show a
requirement for a ground at the terminals, and it does not require a
battery. An identical thermostat unit installed on the bedroom zone is
working correctly. The transformer is rated at 24V so that rating
should be fine with these thermostats. I have been monitoring excatly
what seems to be happening: The display is on and showing the current
room temperature. When I turn the dial to set the heat temp I want for
the room the flame symbol appears and a few moments later the furnace
fires up. After a short period of time the furnace cuts off, and after
another short period the valve closes. When the valve closes, that is
when the display shuts off. Several minutes later the display comes
back on the valve has reopened, the room is not yet at the requested
temperature, and the furnace may fire up again. After a short period
of time again when the valve closes the display disappears again. This
continues until either I switch the required setting to below the
current room temperature, or when the room reaches the heat setting. I
tried swapping the front panel from the bedroom zone, and the same thing
happens. I am trying to determine whether the fault lies with the valve
which is a few years old (not sure quite how old), or whether there is a
fault with the thermostat before I go to the expense of replacing one or
the other. Your suggestions are most welcome.
RBM Wrote:
This thermostat doesn't require a common, just the two wires. I would
look
to the wattage of the transformer that's powering the three zone
valves
"Achattaway" wrote in message
...
I have three heat zones in my home, two upstairs and one in the
basement. I recently upgraded my old mercury Honeywell thermostats
upstairs to a digital type CT8775A. They are connected to Honeywell
motorized valves at the boiler, type V8043E1012.
When I installed the thermostats I was careful to map the wiring and
everything seemed fine, the digital display came up, the room temp
was
monitored and the backlight was working fine. However, now that I am
starting to need the heat the problem occurs. When the room is above
the temp of the thermostat setting everything is fine and the display
works. When I raise the temp setting on the thermostat to turn the
heating on, and after the furnace has fired up, the display goes
blank,
the backlight doesn't work but the furnace continues to burn. When
the
furnace switches off afet a couple of minutes the display reappears,
only to disappear again.
I have tested the wiring connections at the boiler and behind the
thermostat and they are all good. I have manually overridden the
valve
and tested the motor which appears to spin up OK. I don't know where
to
look next. Has anyone else had the same problem or can anyone
suggest
what the problem might be?
--
Achattaway
--
Achattaway