High Temperature Boilerů Aquastat? also... possible leak


Old 05-22-12, 07:24 AM
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High Temperature Boilerů Aquastat? also... possible leak

I have a hydronic, oil fired, Slant Fin Liberty L-30-PT boiler with tankless coil that was installed in our home in 1994. The Honeywell L8124c Aquastat seems to be malfunctioning because the temperature of the boiler is much higher than what's specified by the aquastat's settings.

With the Aquastat HI setting set to 160║F, when the thermostat is turned on the burner starts at 188║F and shuts off at 210║F. There's a lot of crackling, popping and sizzling when it gets up to 195║ or so. Even after the burner shuts off, the heat soak brings it up another 20║ to 30║, so if the circulators turn off at this point it's not uncommon to see the boiler reach up to 240║F. It makes a lot of noise here, but calms down after a while. The pressure doesn't exceed 25psi on the gage. The relief valve hasn't recently released.

With the LO setting at 140║ (the DIFF is set to 10) when domestic hot water is run, the burner comes on at 160║ and shuts off at 180║

This boiler has always run hotter than the aquastat settings, and when the boiler was first installed, about three months after it was installed I called the installer about this and he came out and installed a new Aquastat, and said he'd never seen that problem before. But the new one he installed was only slightly better. He said I should just keep it set lower by 20║ than what I want it to do.

For years that was fine, except when the annual cleaning is done by our oil supplier, they always reset the the settings to 180 and 160. They start the boiler to check it the temperature, gas and soot readings from the stack, but never watch to see how high the temperature of the boiler goes. This last time, when I told the technician, he saw it went higher than it should but simply turned the settings down to 170║ 150║ (which is still too high).

I also have checked the boiler temperature with a digital infrared thermometer to verify the accuracy of the boiler thermometer. I took the reading from the top of the boiler where the outlet pipe comes out. The temperatures were within 1║ of each other.

There is another "situation" with this boiler that may make this whole issue moot. I'll post that issue, (possible leak or crack in the boiler) in an adjacent post because it is different, although could be related.

Any comments or suggestions would be greatly appreciated.

Last edited by NJT; 05-22-12 at 04:49 PM.
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Old 05-22-12, 07:28 AM
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Red Powder On Boiler (Slant Fin)

This question is related to the adjacent post about the aquastat on our hydronic oil fired Slant Fin Liberty L-30-PT that was installed around 1994. We just had the boiler's annual cleaning done, and the service technician thought there may be a leak in the boiler. This, because he noticed fine red (rust colored) powder that had "puffed" out of the stack where it connects to the flue collar on the top of the boiler. He suggested a replacement boiler.

However, there is no visible water leaking from the boiler. After he left, I took a flashlight and mirror and looked into the firebox through the observation port, and to me it looks like there has been a leak next to the tankless hot water heater area on the bottom of the cast iron boiler. There is crusted rust with small white staining on the cast boiler directly above where the flame shoots out.

Inside the firebox in general, has a fine covering of this rust colored powder, mostly on the side nearest the tankless water heater area, where about 1/8 inch of dry, rust colored debris looks like its running down that side of the firebox.

The boiler doesn't seem to lose pressure because I've turned off the water feed to see if it reduces over a few days. Over four days it has not. It doesn't appear to be leaking currently, but has obviously leaked in the recent past. I have not noticed any staining or water on the floor.

I've been wondering if the boiler running hotter than it should as discussed in my "Aquastat" post could cause something like this? And, can a boiler "heal" a leak, or is it sure to reappear during the worst part of the next heating season?

Any comments would be appreciated. Thanks

Edit: Update,
I just returned from Home Depot while looking for some thermal paste for the aquastat, and saw they had an opened up similar Slant Fin Boiler there. The area where mine was apparently leaking looks like it would be where the seam of the cast boiler pieces fit together. My boiler did have a cool down last Fall, when we lost electricity for 5 days in early November. Maybe it was then that it loosened up.

Last edited by don48mac; 05-22-12 at 10:25 AM.
Old 05-22-12, 04:45 PM
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He suggested a replacement boiler.
Yes, of course he did. I'm sure he gets a handsome commission for every sale he scares a customer into.

Don, I've merged the two threads back together again. I think it will be easier to keep track of this way...

More later.......................
Old 05-22-12, 04:57 PM
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Thanks. I wasn't sure if I should put them together or not.

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