Boiler shuts off - Overheating?


Old 02-15-18, 08:53 AM
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Join Date: Feb 2018
Location: USA
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Boiler shuts off - Overheating?

I work at a church/school and they have this old school boiler in one of their buildings. The boiler seems to be overheating as it works fine and then shuts off once it peaks at 220F.

Had a "boiler specialist" come out last week and all he did was hit the reset which ignited the fire and turned it on again. The next day it was already off. So yesterday I reset it myself and it kept shutting off at 220F.

Nothing is set that high so I take it there's some sort of clog or faulty part in the system. The guy mentioned it might be a bad aquastat. I am super unfamiliar with this system and boilers in general. I've been trying to watch videos and read around yet I'm still lost.

I'd greatly appreciate any advice!

See pics attached, I can take more (warning they are huge)
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Old 02-15-18, 11:05 AM
Join Date: Oct 2013
Location: United States
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You posted pics of 2 controls. With the limited info I'm guessing one is your operating control and the one with the red reset button is your safety high limit.

That safety is there in case your other control malfunctions and stops the boiler from running dangerously high and not shutting off at all.

The 1st control looks like it's set at 155. If there are no other controls that is the one that sets your maintaining temp.

What you can do is with a screwdriver turn that controls temp up and down and see if it responds. That is the control that turns the boiler on & off. If not then it must be replaced.

It sounds like it's not shutting off at 155, but reaching the high temp of the manual safety control which means that control is working fine.

What you can also do is lower the temp setting of the high safety high limit control to about 200 to see if it shuts the boiler down earlier, then you'll know if that control is what is shutting the boiler down. There is nothing dangerous about the high temp your boiler is reaching.

What is dangerous is the operating control not working correctly.

More pics of any other controls would be helpful and you might want to look at your relief valve tag and see what it says for pressure rating.

Your gauge is reading almost 30 psi which is high normally if you have a 30 PSI relief valve.

With a boiler that size though you may have a 40 or 50 psi relief valve so the pressure you have would not be an issue.

Hope this helps a little.
Old 02-15-18, 11:31 AM
Join Date: Jan 2017
Location: USA
Posts: 487
You show a control set at 155 degrees . That is probably the control that is not working properly. (the one without the reset button). It should me mounted in a brass well which would allow you to replace the control without loosing any water. However, before you try to replace the control you should post a better picture of the whole control since the whole device can't be seen and you need to show the name and model of the control. Is the building overheating or under heating? What controls the operation of the boiler and the circulating pumps? The pressure gauge is reading 30 psig. that is too high. You probably need the expansion tank serviced and maybe a new PRV. How high is the building/? (how many floors above the boiler are there)? That boiler is rated at a maximum pressure of 30 psig.
Old 02-15-18, 12:44 PM
Join Date: Mar 2006
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"With a boiler that size though you may have a 40 or 50 psi relief valve so the pressure you have would not be an issue".

The boiler name plate states 30 lbs as maximum working pressure for water.
Old 02-15-18, 03:52 PM
Join Date: Oct 2013
Location: United States
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Missed that Furd. If it was any bigger it would have bit me.

I guess they have a point when they say why don't you put your glasses on.

Old 02-16-18, 02:26 AM
Join Date: Jan 2017
Location: USA
Posts: 487
A word of CAUTION; I would not work on this boiler , even as an employee, since it is in a commercial building. Depending upon the codes in your area, only licensed HVAC service companies with liability insurance should do anything to this unit. I attend a church in my area and I refuse to work on any of their heating equipment since I no longer carry "liability insurance". If you make a mistake , the insurance company that insures that boiler will be looking for someone to blame. If you touch it it's yours. I can tell them what they need and make sure the company that does the work does a good job. That is it "just a word of caution"

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