Boiler Temperature Setting Question

[n2ah]

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.

Thanks, Art Harris

[Pj]

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.

Pj

[shebaaa]

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 tankless coil

[Paul Flansburg]

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.

-paul

[Edwin Pawlowski]

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 the thermostat.

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.

[n2ah]

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.

Art Harris

[Doug Miller]

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 problems.

Of course, if you have a digital thermometer available, that's probably the preferred tool to use. :-)

[Seth Goodman]

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! ;-)

[Paul Flansburg]

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?

-paul

[n2ah]

I just had a leaking 8-year-old Burnham V73 block replaced under warranty with the V83. That's why I'm looking closely at everything.

Yes, plenty of hot water (my wife says it's _too_ hot). I'm just trying to make sense out of what I'm seeing, and be sure there isn't a problem. Sounds like all is well.

Art Harris

[Paul Flansburg]

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.

-paul

[Doug Miller]

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 temperature swings.

[Abel]

replying to n2ah, Abel wrote: how do you set TIC in the boiler