Boiler reaches high limit within minutes, then shuts off

fuentesfern

Hi all, new to the forum and I am posting in hopes that someone could help me out with my boiler problems. So back in December I went to turn on my boiler for the first time in this winter and found that after the pipes made some noises the boiler shut down. After investigating a bit I determined that the issue was that the boiler was reaching the high limit on the aquastat very quickly and then shutting off as it's supposed to. I didn't think that was the normal function of the boiler since the house will never get warm like that. I PSEG tech came to check the boiler and for $ told me that the problem was lack of flow and the culprit was a bad circulator pump. Instead of paying the $ for replacing this item I bought a new pump for $ and replaced it myself. I thought that would solve the issue but when I turned on the boiler again nothing had changed. The temp and pressure shoot up and reach the safety limit within minutes and everything shuts down. I can tell that the new pump is working (low humming) so I think that eliminates that possibility. However, I guess there is still some circulation problem somewhere. To tackle that possibility I tried bleeding the system of air since I read air lock could be the cause. In the attached diagram, you can see that there is only 1 place 1 can bleed the system by opening the spicket with hose in my diagram. None of my baseboard heaters have bleeder valves so I can't bleed those individually. So here is what happens when I open the spicket: if the red valve in my diagram is closed no water comes out, if that same valve is open, hot water comes out, and if the valve is closed but I manually open the auto fill valve then cold water comes out and the boiler temp and pressure go down. This to me seems like there is no circulation when the system is closed but I just changed the pump so how can that not be working? Air lock is also not likely since when I open the autofill valve i get water going completely through the system and coming out of the bleeder hose. What am I missing and what can be the issue? Many thanks for your help!!

STEVEusaPA

Just because you hear humming, doesn't mean the circulator is circulating water.
Is the water coming back to the boiler (about 10 feet away) almost as hot as the water leaving the boiler (also about 10 feet away)?

Jamie Hall

Double check, please. If you close the red valve and then open the drain spigot, no water comes out? And if you then open the red valve -- change nothing else -- then water does come out?

If so, then indeed water can't circulate. Don't try to run your nice new pump -- you'll likely ruin it. Instead, trace all your pipes carefully and see if somewhere, lurking in a corner, there is a valve on either the hot water feed to the radiators or the cool water return which got closed somehow.

fuentesfern

STEVEusaPA said:

Just because you hear humming, doesn't mean the circulator is circulating water.
Is the water coming back to the boiler (about 10 feet away) almost as hot as the water leaving the boiler (also about 10 feet away)?

I have not checked more than a couple of feet away and I figured that the return pipe would be hot just due to convection.

fuentesfern

Jamie Hall said:

Double check, please. If you close the red valve and then open the drain spigot, no water comes out? And if you then open the red valve -- change nothing else -- then water does come out?

If so, then indeed water can't circulate. Don't try to run your nice new pump -- you'll likely ruin it. Instead, trace all your pipes carefully and see if somewhere, lurking in a corner, there is a valve on either the hot water feed to the radiators or the cool water return which got closed somehow.

I'm pretty sure that is the case but I will double check tonight. I can't imagine any other valves anywhere else in the system other than in the boiler room.

Jamie Hall

fuentesfern said:

Jamie Hall said:

Double check, please. If you close the red valve and then open the drain spigot, no water comes out? And if you then open the red valve -- change nothing else -- then water does come out?

If so, then indeed water can't circulate. Don't try to run your nice new pump -- you'll likely ruin it. Instead, trace all your pipes carefully and see if somewhere, lurking in a corner, there is a valve on either the hot water feed to the radiators or the cool water return which got closed somehow.

I'm pretty sure that is the case but I will double check tonight. I can't imagine any other valves anywhere else in the system other than in the boiler room.

Point is, if water can circulate then it doesn't matter whether the red valve is opened or closed when you open the spigot -- water should come out.

Another possibility -- other than a closed valve -- is that your system for some reason doesn't have enough water in it to rise from the boiler up to your radiation, then flow around and come back down. Hard to believe that is the case, but... the comment you made about the pressure dropping when you open the autofill valve by hand does give me pause... doesn't make much sense.

JUGHNE

How about a picture of your new pump? Both sides and the nameplate.

rick in Alaska

Did you make sure the new pump is installed in the same direction as the old pump? You can't go by the way the control box is positioned because it may have been rotated when the last person installed it. If it has a check valve in it, that would stop the flow if you are trying to feed it backward.
And make sure you have at least 8-12 psi for boiler pressure.
Rick

mattmia2

is this a single zone? does the thermostat come back to the boiler control?

mattmia2

How much water did you flush out of the boiler drain before the red valve with the red valve closed and the fast fill open? You may have air trapped in that loop from when you replaced the pump that you need to purge out. It may take several gallons.

What pressure does the system come up to when you close the fast fill and let it come up to pressure?

by "the temp and pressure goes down" you mean the pressure goes down as soon as you open the fast fill valve, or the pressure actually went down when you opened the boiler drain before the fast fill valve?

It kind of sounds like the pressure reducing valve or water supply is not keeping enough pressure in the system to keep the air out and keep it circulating.

Gordy

How much water did you have to drain to replace the circulator?

unclejohn

We need pictures gol dern it.