Furnace water temperature above its setting

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Old 10-30-13, 02:00 PM
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Furnace water temperature above its setting

I have an oil burning Burnham furnace with a Honeywell Triple Aquastat -Relay L8124A, C. The hi setting is set for 180 degrees and the low is set at 170 degress and the differential is set at 10 degrees. The furnace is working, going on and off but the high temperature is going up to 210 degrees and 20 PSI. My water is now burning us. This happened all of a sudden and has been like this for a week. Do I assume the aquastat is bad and replace it?

Thanks for your help,
Keith Duke
 
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Old 10-30-13, 02:57 PM
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Hi Keith,

First thing... may not have anything to do with the current problem since you say it's been this way for years... but the HIGH and LOW settings must never be closer than 20 apart. (there is fine print on the white part that the dials is on that says this, by the way) So you should lower the 170 to 160 ...

Differential should also be higher, typically 15-20 and this would give a little more hot water...

But this is still nothing to do with your problem.

It is possible that your aquastat is starting to 'drift'... try turning the LOW down to 150, the HIGH down to 170 and leave the DIFF at 10 for now, and observe what happens for a day or two.

Does your system have the large steel tank in the floor joists above the boiler? Or is your expansion tank the type that looks like a propane gas grill tank hanging from the pipes?

You might want to read these for informational purposes:

http://www.doityourself.com/forum/bo...sion-tank.html

http://www.doityourself.com/forum/bo...ure-gauge.html

Because sooner or later you will need to know this.
 
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Old 10-31-13, 06:17 AM
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Thanks for the quick resonse!!

I'll try turning down the temps tonight and will keep a 20 degree differential for the future. I have expansion tank that looks like a propane tank hanging from the ceiling. I checked the pressure in the tank and it was 9 PSI, I kind of remember it was around 15 PSI when I installed it about a year ago. When it went the pressure relief value would open and but this is not happening now. Should I increase the pressure in this tank? When I tap on the tank it sounds like there if half air and half water in the tank, when I had to replace it tank it was full of water.

Thanks again, your expertise is greatly appreciated!
Keith
 
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Old 10-31-13, 06:34 AM
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Hi Keith,

Should I increase the pressure in this tank? When I tap on the tank it sounds like there if half air and half water in the tank, when I had to replace it tank it was full of water.
That tank should be checked at LEAST bi-annually.

Yes, the pressure in the tank should be 12 PSI minimum, as should the boiler pressure when the system is cold.

Understand that reading the pressure on the tank when there is pressure in the system will not give an accurate indication of the actual pressure in the tank. You MUST follow the step by step directions in the post that I linked to in order to properly set the pressure.

I don't put much stock in the 'tap test' for determining how much water is in the tank... don't forget that there is a rubber piece inside that tank as well... and can give a different 'sound' on either end of the tank.

Again though, these steps are just routine preventative maintenance and likely NOT related to the overheating issue... which can be a fairly serious issue... so don't let this other stuff take your focus off getting that fixed FIRST!
 
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Old 10-31-13, 10:13 AM
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Thanks

I'll reset the expansion tanks pressure and make sure it is not full of water tonight and change the temps on the aquastat. I'm thinking of ordering a new aquastat from PexSupply today as I'm afraid not to have one if that's the problem and the thing completely quits during a cold night. I'll check out Pex's return policy first. Does that sound like a reasonable thing to do with the issues I'm having? I also wanted to tell you what I did a couple of nights ago to the aquastat and neglected to mention. For several years the aquastat was set at 190 degrees for the high and 180 for the low. A few nights ago I changed it to a 180 F high and a 170 F low to see what happened to the high temperature. It came down a bit from the 210 F it was running at to about 195-200 F which is still burning us when we run hot water.

Thanks Again!
Keith
 
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Old 10-31-13, 02:57 PM
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Here's something to check... the temperature sensing bulb needs to be fully inserted into the boiler's immersion well. If for some strange reason it has slipped back out it can account for some inaccuracy. Be very careful when working with aquastats to NOT put a 'kink' in the capillary tube. If you do, it's done.

I'll check out Pex's return policy first.
Yes, good idea. I think they would let you return it in UNUSED condition within a reasonable time limit.

A few thoughts about your hot water... Think about having a THERMOSTATIC TEMPERING VALVE installed on the hot line going to the house. This will prevent scalding injuries and is CODE in many jurisdictions in these 'modern' times.

Pretty good article here:

Thermostatic Mixing Valves - The Dangers of Hot Water and Scalding - Learn About - Watts

Watts isn't the only manufacturer of course... Taco, Honeywell, and many others...

During the summer, when the boiler is not heating the home, the aquastat is operating strictly off of it's LOW LIMIT. Water to the taps can be no hotter than that temperature.

Once the boiler starts working to heat the home, if you go to draw hot water when the boiler is working on a heat call, the HIGH LIMIT is what controls the temperature and you could have hotter water.

For several years the aquastat was set at 190 degrees for the high and 180 for the low. A few nights ago I changed it to a 180 F high and a 170 F low to see what happened to the high temperature. It came down a bit from the 210 F it was running at to about 195-200 F which is still burning us when we run hot water.
So turn it down more...

Something else to look at too, watch the system during a heat call. Make note of the temperature that the burner actually kicks off. One thing that could be part of what you are seeing is what I call 'heat soak', where the heat that is trapped in the cast iron at the end of a heat call continues to transfer to the water in the boiler. If your thermostat satisfies and stops the heat call with a hot boiler, the pump will stop also. Since the water in not moving through the boiler the heat in the cast iron can push the water temps up to 200-210 easily.

So try to determine if the burner actually DOES kick off at the correct temp, and you are simply seeing the 'heat soak' thing going on...
 
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Old 10-31-13, 03:42 PM
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the temperature sensing bulb needs to be fully inserted into the boiler's immersion well.
It's a good idea to bend the capillary tube SLIGHTLY, just enough to that the bulb physically contacts the inside wall of the thermowell. Also, daub some heat conductive compound (such as Honeywell #107408) on the bulb before inserting it into the well to improve heat transfer. Sometimes a small tube of heat conductive compound comes packaged with an aquastat - if not, you'll need to buy it separately.
 
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Old 10-31-13, 03:50 PM
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I don't care for that stuff Gil... tends to dry and harden over time and 'glue' the bulb into the well.

If used, then just a 'little dab'll do ya'. Only at the bottom of the well on the end of the bulb. If the well is spooged up with the stuff chances are that you either will not be able to get the bulb fully into the well, or you will never get it out again years later when you need to.
 
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Old 10-31-13, 04:33 PM
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I don't care for that stuff Gil... tends to dry and harden over time and 'glue' the bulb into the well.
I haven't noticed any problem yet, and I replaced my aquastat recently. But if it is a real problem, I will notice soon, given my usual theory that "if a little does a little good, a lot does a lot of good."

The next time I pull my aquastat, I might use my shotgun cleaning set to clean out the thermowell. A pass or two with a brass brush (20 gauge?), a patch with Hoppe's #9, and a few dry patches.
 
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Old 10-31-13, 04:57 PM
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More like a .410 I think..................
 
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Old 11-01-13, 07:28 AM
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I turned the settings down to 170 high and 150 low at lunch yesterday and watch the heating cycle last night. It turns on at 150 and off at about 180. This morning the water temperature was more in line with the way it was before it got really hot. I did not have time to properly set the pressure on the expansion tank last night but I did press the air valve and only air came out so I think its good, I'll set the pressure correctly tonight. I will also pull out the aquastat to see how the probe looks.
Thanks!!!
Keith
 
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Old 11-08-13, 05:26 AM
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I reset the temps on the aquastat to 170 high and 150 low and changed the differential to 15 degrees. I also checked the expansion tanks pressure and reset it to 12 PSI. I have been watching the temps for a few days, they run from about 150 degrees to 180 and 10 to 20 PSI. I purchased a new aquastat from Home Depot but have not installed it. The local plumbing supply house had the aquastat for about $100.00 more than the Home Depot, I wonder if they get a cheaper version like they do with most brands, any thoughts on this. The faucets still get a bit hotter than they used to but the handle settings are the same as before I had the very hot water issues. When the water was very hot the faucets only had to be turned on about 1/4 turn, now they are back to the 3/4 of a turn where they used to be. I think it seems to be performing properly now, any thoughts? Not sure if I should return the aquastat yet.

Thanks for your help!
Keith
 
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Old 11-08-13, 02:21 PM
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The local plumbing supply house had the aquastat for about $100.00 more than the Home Depot, I wonder if they get a cheaper version
To my knowledge, they are all the same. HD deals in volume so can cut a closer profit margin than the small supply houses.

I think it seems to be performing properly now, any thoughts? Not sure if I should return the aquastat yet.
If all seems OK for now, give it a wait and see what happens. Your call on the a'stat...
 
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Old 11-12-13, 07:25 AM
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Thanks for your assistance, I'm going to hold onto the aquastat for awhile and may install it to see if there's a difference.
On a separate topic, I have watched the furnace getting cleaned before and I'm considering doing it myself. Do you have any instructional videos etc. on doing this. I would also like to know if you know the size and a source for getting cleaning brushes for this. Its a Burnham furnace.
Your help is greatly appreciated!
Keith
 
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Old 11-12-13, 04:27 PM
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Do you have any instructional videos etc. on doing this
No, I'm sorry that I do not. Every boiler is different.

Please understand that in addition to cleaning the boiler that the burner must also be serviced. Even if you clean it, there is other stuff needs done also!

What's the model? Burnham has dozens...
 
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