Another Boiler Temp Question


Old 01-21-08, 02:47 PM
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Another Boiler Temp Question

I have a 50+ year old Weil Mclain OB15 boiler. And thanks to NJTrooper it is functioning very well.
My question is how the 2 aquastats work. The one located in the boiler is set at 180 and the one outside on top is set at 200. I assume the 200 is the max limit. Does this translate to it stays between 180 and 200. I am located in Rhode Island. Are these good temps. The heat seems to work well unless it is unusually cold like single digits. BTW the temp gauge on the temp/pressure gauge is broken.


Last edited by NJT; 01-21-08 at 05:38 PM.
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Old 01-21-08, 04:42 PM
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Without knowing exactly how the two controls are wired it is impossible to state what each of them does.

It is possible that the one strapped to the pipe is a secondary high limit safety control.

BTW, the wiring to that control in the lower picture needs to be repaired.
Old 01-21-08, 05:07 PM
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The black unit on the pipe is connected to the emergency switch on the side of the boiler by 14g black wire and appears to be line voltage, The unit in the boiler is connected by 2 wires to terminals T1 and T2 on the burner relay box. Helpful?
I will ask the service guy to handle the wiring on his next service trip...nice catch. It looks worse in the picture than it really is.
Old 01-21-08, 05:42 PM
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furd is probably correct... those controls 'pre-date' me !

I'm pretty sure that the black one probably has a mercury capsule inside... if it ever needs to be disposed of, please do so responsibly!

Angelo, it appears that there was at one time a 'stack switch' on the flue pipe, has the unit been retrofitted with a modern burner with a cad cell ?

You mentioned in the other post that you were considering going with natural gas in the future, and looking for recommendations. Are you thinking about retro-fitting this boiler with a gas burner ? or an entirely new system ?
Old 01-21-08, 06:07 PM
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You are correct there is a big mercury capsule inside. as far as the burner, does the picture answer your question?

As far as the future upgrade, I intend to replace the entire boiler with gas but do not intend to make any changes to the radiation. I have a combination of new baseboard and some older half in the wall copper/fin radiation, mostly under windows. Fairly adequate since the house was built in the late 40s with no insulation and have since had blown in the walls and a new second floor(cape style) 2 years ago with insulation up to current codes.

Last edited by NJT; 01-21-08 at 08:04 PM.

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