I have a old boiler furnace. I'm having an issue where the boiler
periodically wont come on and the house temperature will continue to
drop. If I turn the thermostat up, the boiler will kick on and will
maintain the set temp for some time but will eventually fail to kick
on again. Based on the fact that I can get it to kick on by
the thermostat, I'm assuming the issue is thermostat related but I'm
not sure if the thermostat itself of the sensor...or maybe I''m
totally off base.
On 5 Apr 2007 19:25:23 -0700, email@example.com wrote:
And then to get it to go on, you turn it up even higher, or you turn
it down and turn it back up again? Or do both work?
OR the sensor? The sensor in the thermostat, right? I might, but
very few people would try to repair the thermostat, so if you mean a
sensor in the thermostat, you might as well replace the thermostat.
...or maybe I''m
Another way to verify this is to note that that the thermostat
connects two wires together. You can take the stat off the wall, and
if you figure out which two wires they are, you can touch them
together and see if the boiler goes on immediately. If you only have
two wires (no AC) it will be easy to tell which two wires they are.
When the stat is totally disconnected, you can also use an ohmmeter on
the matching screws of the thermostat and see if the stat goes from
infinite resistance to near zero resistance as you adjust the
thermostat near the room temperature.
It's possible that the stat works but is wrong as to temp. If that is
the only problem then you could just learn to add 3 degrees or
whatever from the setting you have it at. This is especially relevant
to my first question above. If you turn the stat to warmer, say to
76, but later on turn it back down to 70, the house might get down to
66 or 67, because the stat is miscalibrated and it thinks 66 is 70 and
67 is 71. If that is the case, just set it to 74, and it won't think
it is 74 until it is actually 70, which for this example is what you
Also, make sure the thermostat isn't getting a warm air breeze or a
lot of sunlight, so it's warmer than the rest of the house. Normally
they are put where this won't happen, but who knows.
Is there any way you can get your hands on another thermostat just to
test it? Or just buy a new one....
Anything is possible, but it does sound like a thermostat problem to
me. If the thermostat is a modern digital type, they can get flakey.
Of course be sure the batteries are good. If it's the old Honeywell
type with the mercury bubble inside, they MUST be level, but the
contacts may be failing, and of course, make sure the mercury did not
separate (unlikely but possible).
From your description, it sounds like it could be a bad thermostat, but
"old" is a relative term. Over the years there have been a number of types
of thermostats and controls used on boilers. The most common type today, is
what Honeywell calls a "series 80" which is low voltage two wire. There have
been series 10 through series 90 thermostats and controls used over the
years. The first thing you need to do is identify what you have. Remove the
thermostat from its base, and if it's for heating only, note how many wires
it has and if they are low voltage or line voltage. Once that's determined
it would be easier to solve your problem
On Apr 5, 10:25 pm, firstname.lastname@example.org wrote:
I have a gas furnace but had the same problem. We had an old
mechanical thermostat that just wouldn't hold a constant
I don't really know what goes wrong with those old thermostats but it
almost seems like they just stiffen up over time and don't respond to
temperature changes fast enough anymore. My old thermostat would also
show that it was 68 degrees in the house when I could *feel* that it
was about 55 at best. Once it did finally kick on, it would run full
blast for hours trying to catch up, and then would overshoot the
target temp because again it was not responding fast enough to the
temperature change. But then when it kicked off, it would stay off
all day again. Sounds like the same problem you're having.
Went out and bought a $25 digital programmable thermostat and the
problem was solved. Good news is thermostats are so cheap and easy to
install that you could just buy a new one as an easy diagnostic. Took
me 20 minutes to install it and required nothing but a screwdriver.
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