I just bought a house with a Rheem forced-air gas furnace upstairs with
an electronic pilot light and a manual thermostat. Here's the problem:
For about 17 hours every day it works fine. Every night around bedtime
it shuts down for several hours and won't restart. I've tried turning
it off and on. It just comes one for a few minutes, blows cold air and
shuts down. Can it be a bad thermostat if it works fine the rest of the
day? I'm confused and need some help. I'd call a service technician,
but he would come during the day, charge me a $100 service call, and
tell me it works fine. Help?
My house is like that too. I think during the day, people are walking
around helping circulate the air and preventing the buildup of static
At night when the air is still, the bedrooms get cold, but the
thermostat (in the hallway) stays satisfied.
I don't have an answer.... That just seems to be the way it works.
That being said, check to see if your thermostat has some sort of
anticipator adjustment. It's supposed to prevent wide temperature
Sounds like it's actually controlled by a programmable t-stat. (Does
your manual t-stat actually control the temp setting at other times?)
Or it's haunted.
Sorry, but your limited understanding of the system, implied in your
question, means that you need to call in someone who can answer your
questions. Provide a full description and list of questions up front,
or arrange to be there to ask personally.
And ... you would benefit significantly from a programmable t-stat,
using setbacks (night and mid-day) as deep as possible. Small price
differential from fixed-setting oldies.
I don't know the brand, but its one of those brown dial thermostats.
I've played with various settings on the heat anticipator with no
results. The t-stat does control the heat and temperature most of the
day. In the evening hours, temperature drops all the way to low 60s.
Sorry J, but if it weren't for my limited understanding of the system I
wouldn't need to ask for help.
I'm going to guess that the anticipator
is set for too short intervals.
Of course, it could be other things
causing the problems too.
As most new furnaces turn the blower on
immediately when the
thermostat calls for heat, cold air will
blow until the heat exchanger
gets hot .... a bad idea, from a comfort
standpoint, IMO. Usually
there is a current rating on the gas
valve or control system, which
is the setting of the anticipator. You
can go a bit "longer" or "shorter"
than that setting, however, not too far.
Too far towards the shorter,
will probably cause problems as you
describe. I usually start at the
rated setting, and adjust from there a
bit, as required. Of course, as
some have said, a programmable unit is
much better. The one I have,
basically, does the anticipation
function in the software (firmware), but
I have seen it turn on and then off,
prematurely, especially when there
is aa outdoor temperature swing
Competent expert who can see your system can help you understand how
your system works; we, at a remove, cannot, except in broadest
Thermostat can only control temp of its location. Is it doing that? For
a couple $, you can get various accurate thermometers from hvac-supply
or big-box. The old Honeywell I replaced with programmable has a
thermometer that's close up to about 67 deg F. Then it doesn't move
until temp is above 75 deg F, whereupon it indicates 68 deg F. IOW,
Other spaces, to be heated controllably, need to be in communication
with system and t-stat. Meaning, for instance, if heated air is pumped
to area of t-stat more so than to other areas, and those other areas
are in poor communication, they will be cooler.
Also, discharges and returns must be designed for consistency from
floor to floor, with heating and a/c. Sometimes kids like to play with
In a different vein:
When you "make" the t-stat, pull the outer cover so you can see the
mercury switch. Do you see the mercury surge to cover the contacts?
The burner should now light. Depending on the setting of the fan
switch, when the heat exchanger warms up to fan-switch set-point, the
fan will start. Later, t-stat will open, burner stop, furnace cool and
fan to off. Easy enough to track this sequence.
When you drop the setting so that the mercury surges the other way, do
you see a small arc as the contacts open?
This sounds like something I would intentionally do to save on heating
costs. i.e. Program the thermostat to go down to about 60 in the late
Find out the brand and model number of the thermostat. And the brand and
model number of the furnace. Next find the instruction manuals for these -
perhaps on the internet. Or ask here. If you are brave, ask on alt.hvac, but
you would need to give them brands and model numbers...
"dave" wrote in message
Maybe beachcomber is right. Regardless, have you tried turning the
setting up at night, to 75 or 80?. 85?
OR: They make little heaters, on timers, that go underneath the
thermostat, as a way to have a setback effectt without changing the
themostat. Maybe you could do the opposite. Take a bag of frozen
vegetables and hold it around the thermostat until the air inside gets
colder. Does the furnace go on then?
If not, I guess I would try to debug the system as if it were always
broken. The first step in that is, I think, bypassing the thermostat
by shorting two of the wires together, as if the thermostat was
calling for heat. I don't know about colors though, which wires to
short.. You can also find the same colors at the furnace.
Maybe at night it gets cold somewhere and a broken wire causes an open
circuit, but in the day this doesn't happen. This doesn't sound
likely but neither does your situation. Like I say, learn how to fix
it in general, and do so at night.
(My mother had a Zenith tv that was good for more than a decade, but
once it broke. It was a tube set. Everytime I visited from out of
town, the tv worked so I couldn't fix it. But one time I came home
without telling her, and I tricked the tv. Caught it not working.
All it was was a loose pin clip for one of the pins on the tv tubes.
Worked well for years after that.)
Hack into his sytem and change his clocks by 12 hours. Then he'll
come at night..
Remove NOPSAM to email me. Please let
me know if you have posted also.
The thermostat is simply a switch; inside it is a bulb with some
contacts and some mercury that rolls back and forth inside the bulb to
make and break contact as the bimetallic spring that holds the bulb
expands and contracts with the ambient temperature. One can remove the
thermostat, twist its 24 volt red and white wires together to get heat
without any control - just ON.
The furnace's gas valve is opened by power from the thermostat, the
furnace lights and when the fire box is warm the blower for the ducts
will start to distribute the heat. The fire is cut off when the
thermostat switches to OFF and the furnace blower runs until the fire
box cools down when it shuts off.
That's basically how it works.
You said the furnace was upstairs. Is there another furnace for
downstairs? If so are there timers on either furnace?
You have one of the strnagest problems I have seen posted on here.
You dont by chance have one of those electrical services that was
inteneded to turn an electric water heater on and off by the electric
company. I have mostly only seen those used in rural areas, but
anything is possible. Be sure you have 120VAC power to the furnace
just in case someone wired to some special circuit like this, or even
a light times installed into your system. Once you prove you have
120VAC going to the furnace, you need to take the thermostat off the
wall and short across the wires. (I's just low voltage, and wont hurt
you). If the furnace starts, you need a new thermostat. (or
thermostat battery, although I have never seen a manual obe with
I'm assuming this is a house, not an apartment or condo, where
something could be controlled by a neighbor thru mis-wiring it.
One other thing, are you POSITIVE thats not a setback (programmable)
If this dont do it, you probably do have a ghost and need a priest !!!
Thank you for all the advice. It is an old Honeywell manual thermostat.
Indeed there is power to the furnace, with a switch box. The furnace
was installed 1992. I have watched the burner sequence many times. The
thermostat is indeed calling for heat as it should. The ignition is
firing red hot, but it doesn't appear to be getting gas for those
several hours. This is what made me think it was a gas pressure problem
upstairs at peak hours (when people are at home in the evening), but
that may be ignorance on my part. I have looked all over for the timing
mechanism that could explain the problem but can't find it. There is no
wiring that would explain it.
I'm beginning to like the ghost explanation. Anyway, my wife is pulling
her hair out. And you can imagine what no heat at bedtime is doing for
the more personal aspects of my life. Argh.
Not that it will help you, though. If the igniter is coming on it
sounds like any pre ignition interlocks are OK. Can you hear the gas
valve solenoid clicking? It should attempt to light a few times (with
a delay between attempts) before it shuts off and resets the sequence.
Could be flaky ignition module or gas valve, would need to check
voltage to solenoid when it's trying to light.....
Yes and no. Most houses have their own pressure regulator, and meter.
HOWEVER, some older sections of Chicago have neighborhood pressure
regulators, I remember the news stories when one failed, and all the gas
appliances in that neighborhood shot out huge jets of flame. So check
and see if you have a meter and regulator setup. If you don't have your
own regulator, then call the gas company and report the problem, and see
what they say, because then what you think may be true.
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