The thermostat settings currently are LO = 130F and HI = 160F. But the
furnace comes on when the water temperature guage reads 160F, and shuts
off when the temperature gauge reads 185F. The temperature gauge
continues to climb to about 190F after the furnace shuts off, due (I
think) to the lag time for the water temp to stabilize.
Does this sound normal? Why doesn't the temperature gauge track with
the thermostat settings? Should I lower the settings?
This is a Burnham V83 boiler in an oil / hot water heating system with
a coil inside the boiler for hot water.
I'm going to take a guess at this one since without additional
information it's too difficult to diagnose the problem: The thermostat
that controls normal on-off functions isn't working and the furnace
stays on until the temperature reaches the "fail safe" setting for
shutdown. In other words, the safety device that prevents the boiler
from popping the pressure relief valve or blowing it's seams is
activating; not a good choice for shuting down the system.
Call the service company that installed the furnace.
Aquastats get off with age and the settings are then adjusted by
Temperature/pressure gauge and not by numbers on the Aquastat. The on
and off Temps you say it is cycling at are fine especially if you have a
All wrong answers......Take a look at the aquastat. This is NOT a
thermostat, but an Aquastat for maintaining the operating temperature
of the boiler. There should be 3 dials on the aquastat. Lo and hi
cutoff and the differential setting. It sounds like the diferential
dial setting is set at 25. This is not a problem!!! Figure out which
manufacturer you have, most are Honeywell, and do a google on the
manufac. and model number. All of your questions will be answered once
you find the correct document.
Thanks for your reply. The Aquastat is a Honeywell Model L4081B. I
googled and found the data on it.
My unit only has two dials, HI and LO. The manual states that HI sets
the boiler temperature, and LO controls the circulator. It doesn't
describe how to set the "differential" temperature.
My question still is: With HI set to 160F, why does my gauge show
temperatures as high as 185F? The diagram in the manual shows that the
burner shuts off at the HI set point.
I suspect either the aquastat or the gauge is defective. To get a quick idea
of which it is, put your hand on a radiator, briefly, while the circulator is
running and the gauge reads 185 -- 160 is pretty hot, but 185 is damn hot. If
you can keep your hand there for a little bit without much discomfort, then
I'd suspect the temp is really 160, and the gauge is faulty -- but if you
immediately jerk your hand back and yell "S**T! That SOB is HOT!!" then the
gauge is probably accurate, and you should be checking the aquastat for
Of course, if you have a digital thermometer available, that's probably the
preferred tool to use. :-)
Doug Miller (alphageek at milmac dot com)
Art, There are tolerances in everything.....You have a built-in
differential of 10 degree's on the HI limit. That puts you at 170
degree's to start with. Then, there are tolerances built into the
temp. gauge. So, with a stack up of all of the tolerances and the
differential I'd say your okay.
Questions: Is there an actual problem with the boiler that made you
look into the temperature gauge? OR did you happen to notice that the
temp. and the settings were not making sense? If there's an issue,
then let's talk about it?
Do you have plenty of heat and hot water?
Does the boiler fire on and off smoothly, no bangs, hesitations, smell
of oil or smoke?
The most important item you need to understand is that your boiler is
NOT a cold fired boiler. What this means is that you need to maintain
at least a temperature of somewhere in the oder of 140 F. Having the
boiler continuosly go from 0 F to operating temp is not good for the
seals. You have a cast iron boiler, and if I remember correctly it's
probably a 4 section. The seals are what make the connection between
the sections and the seals do not like to expand and contract with
large temperature swings. The reason why I mention this is because you
mentioned that your previous boiler leaked.
Is your domestic hot water made by a tankless coil? If so, adjust the
tempering value. If this doesn't work, replace it! Probably cost
about $10 or so dollars and your time.
There won't be much left of that boiler if it ever gets down to 0 F !!
And I suspect that the homeowner would notice that the house was intolerably
cold long before it got even close.
The water returning to the boiler from the radiators can't possibly be any
colder than room temperature (typically about 68 F), which limits the possible
temperature swing to a little over seventy degrees if the operating temp is
set at 140 F. In practice, the temperature of the return water is much, much
higher than room temperature, and the temperature swings experienced by the
boiler are correspondingly smaller.
I very much doubt that the leaking was caused by one hundred forty degree
Doug Miller (alphageek at milmac dot com)
No, your furnace should not come on because of the water temerature. It has
nothing to do with it. What? You don't have a furnace? Right, you have a
boiler. Boilers heat water or make steam. They do thes with burners.
Furnaces heat air.
But your thermostat should be set for a comfort level of about 66 to 70
degrees. You'll never get the house up that high no matter where you set
Now, we can talk Aquastats. That is what you have inside the boiler to
measure the water temperature. Yes, the setting are about right.
Before you think I'm just busing your ass about terminology, there is good
reason to use the right terms. It helps to understand how the system works,
what "stat" controls what part of the system. Taking this one more step,
the thermostats for the room temperature does not control the heater. It
just tells the circulator (or zone valves) that you want heat and the water
will start moving through the radiators. It is the aquastat inside the
boiler that is telling the burner to go on and then off again as needed.
The manual for your boiler:
See page 47. Low limit gets set at 190, with 25 degree differential -
i.e., on at 165, off at 190. High limit (emergency) shutdown set at 210.
Sounds like your aquastat is miscalibrated, but has been corrected for
by actual measurement.
It appears your boiler is working as intended. Are you having any
problems? If not, stop messing with it! ;-)
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