How do I adjust a thermostat so that the heat reaches the set temperature?
My Honeywell round thermostat has a bulb with mercury in it and a coil of
metal that seems to control when it makes electrical contact.
When I set the Honeywell bulb thermostat to 68°F, the heat only gets to
about 58°F. Likewise, when I set the thermostat to 85°F, the heat shuts off
when it reaches about 75°F.
This works fine except my husband keeps yelling at me for setting the
thermostat to 85°.
I know the simple answer is to change him but why do thermostats have
numbers on them if they're not even close to those numbers?
Is there a way to adjust the temperature? When I pull the round cover off,
I see a copper pointer on the bottom with etch marks on the plate below but
that pointer is already all the way to the left and moving it to the right
just seems to make the offset error worse.
What's the procedure to adjust a Honewell round thermostat to reach the set
point before turning off?
On Feb 22, 5:07 pm, Glenda Copeland <gscopel...@Use-Author-Supplied-
You have to turn the mounting of the coil spring that the mercury bulb
is connected to. I don't have that type of thermostat any more, so I
can't give you detailed instructions. But, I'm sure others here will,
give them a few hours.
It's probably easier to just replace the mercury thermostat with a digital.
It'll be more accurate and have less temperature fluctuation. The little
pointy thing is supposed to be aiming at whatever current amount the device
it's controlling is drawing. It may be a relay or a zone valve, so you'd
have to know this, then find the thing, then find the label on it where it
give it's current draw. You could just point the thing far to one side, then
see how it affects the temperature, then far to the other side, and make
whatever adjustments you need. Keep in mind also, that Honeywell T-87 yo-yo
thermostats must be level as well. There are marks on it, that you hold a
plumb bob up to ,to properly level it.
The adjustment you are talkig about s called a heat anticipator. RBM is
correct in that is adjusted to the amperage draw of whatever the
thermostat is controlling. The others are also correct in that digitals
are much more accurate, and now a lot of them actually cost less than
mercury bulb mechanical types. Larry
On Feb 22, 6:23 pm, email@example.com (Lp1331 1p1331) wrote:
The heat anticipator is not whats off with that issue, the anticipator
is correctly set to what it controls and controls how wide a swing you
get before the thermostat comes on and goes off, the issue is its 10f
off which happens with those dial units if someone messed with it not
knowing how to calibrate it to the thermometers "temp" or forced it
over to one side. Honywell used to supply with every round thermostat
a little wrench that slips over the nut so you can turn the dial to
get it set to run as the thermometer temp states, its a real real thin
wrench but maybe Ace or a heating supply house has one. Often they
wernt packed in the box so you had to ask and maybe pay 35c for one.
One of mine is off now and I cant find my wrench, its off 6f, but it
works fine with a 2f swing, so get used to it or get a wrench. Now if
temp swings to much from on to off, then look at the anticipator.
Those units are foolproof in design, and would outlast digital, they
are not made anymore because of the Mercury bulb and disposal
concerns. They still make the round style, but took out the mercury.
You can change it to digital therm. on your own. I did it so anyone can do
it. Just don't allow the wires to fall back into the wall. Seeing that
winter is half over, I'd wait until you don't need the heat. Then if you
mess up, it won't matter so much.
Tell your husband that just because it's pointed to 85, it doesn't mean the
air temp is 85. Get a room thermometer and set it near the thermostat.
Then show him the thermometer's reading of the air temp. And tell him to
mind his own business.... he he.
I don't have that particular unit, but on mine, it looks like the is a nut
behind the metal thermo spring that could be turned a bit to calibrate it. What
you need is to turn it in the direction that makes the mercury switch less
level - just a little. If such an adjustment is not evident, bending the metal
where the switch attaches to the thermospring could do it.
The copper pointer at the bottom probably adjusts the difference between turn on
and turn off.
Agree with you and Ransley. First thing is to make sure it's
level. Then if necessary you need a thin wrench that you can hold
the nut with so the mechanism doesn't move while you rotate the dial.
All in all, considering the conveniences of a programmable digital
one, I'd just replace it. Wouldn't it be nice to set the heat back
at night and have it come back up shortly before you wake up?
I agree that checking if it is level is a starting point. If it is
level, you could shift it off level in the correct direction as an
alternative to finding the real thin wrench that is used to change the
calibration. To change the leveling you may have to unscrew 2 or 3
recessed screws to remove the thermostat from the baseplate, and loosen
the screws holding the baseplate to the wall. The baseplate has level marks.
On Feb 23, 7:51 am, firstname.lastname@example.org wrote:
I have nothing against technology, I have all sorts of stuff, the
round honywell is is even in the museum of modern art. Its a classic,
I can adjust it, calibrate it, set anything with ease, now my digital
if I dont have my manual I cant adjust temp swing or calibrate the
thermometer and I dont know where my manual is anymore. My round
Honywell has setback, I set it back, it has advance, I advance it. It
will outlast new stuff.
This doesn't sound like the OP's problem, but I just thought I'd throw
this out as a FYI. About 12 years or so ago, I ran into a round
Honeywell T87 that I had installed the year before, and something had
happened to the mercury. Instead of it being a shiny silver, it looked
like molten lead, and acted about the same. Normally,as soon as the bulb
gets the least bit off level either way, the mercury will roll in the
lower direction and turn the unit off or on. On this, it wouldn't move
until the bulb was slanted all the way, and it moved like a glob instead
of a fluid. For all the temperature control it did, it might as well
have been a toggle switch. I replaced it under warranty. But the really
strange thing was, over a relatively short time, I ran into two others,
both also T87's that were exactly the same way, and haven't seen any
more since. They always say things like that come in threes. FWIW, the
first was on a gas wall furnace, one of the others was on a gas central,
though the call was for the a/c, and the other an electric central, and
I don't remember if it was an a/c or heat call. Larry
replying to Lp1331 1p1331, jeroboambramblejam wrote:
Sounds like the sluggish mercury droplet had oxidized somehow - maybe a
manufacturing defect allowed oxygen to enter the glass bulb... Or possibly
excess electric current was allowed to course through the mercury droplet and
change its physical properties. I think they are rated for ~24 volts AC from a
transformer fed with ~120 VAC... If the transformer input side partially
shorted, excess current could have been fed to the thermostat.
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