Leaky Boiler??

Jeff_44

Last winter I thought I had a small leak in my boiler - I installed a very sensitive gage that reads in ounces and when the boiler was firing, the gage never read much past zero. I read that one way to find out if a boiler is leaking to overfill it during the off season- so I did and I have not seen one bit of water leaking any where - the odd thing is that the gage I installed now shows a negative reading below zero. I guess this shows the gage is working but is there any other way to test for a leaking boiler?

nicholas bonham-carter

leak test

over-filling is the best way to check for a leak. it would be best to fire the boiler just enough to drive out the oxygen, and leave it for several days to show any wet spots on the floor.

i think your good low-pressure gauge is showing you that your boiler is perfectly sized to the radiation--that all the steam it makes is condensed by the radiators, with none left over to raise the pressure. that is a most fortunate situation to be in, which many people here would like to experience for themselves. 

can you see the pressure during the venting part of the initial firing? if there is too much, it may indicate that you need more main[not radiator] venting.

you probably now have a partial vacuum in the pigtail which shows on the gauge.--nbc

AlexR

leaky pipe?

Perhaps you have a leak elsewhere that's allowing steam to escape such that the pressure stays low.  How often do you have to add water, and how much? 

Jeff_44

Replacement water

The boiler is about six years old - I tend to add water every two weeks or so - about an inch or so in the sight glass (of course this is what I remember from last heating season). I've had the boiler over-filled all summer and not a drop of water has revealed itself anywhere near the boiler. If there was a leak in the system, it may be difficult to track down - I guess I could shut off each radiator and watch the pressure on each burn. That would tell me if one rad and its corresponding riser/piper may have a leak. Does that make sense?

BobC

finding a steam leak

Shutting the supply valve on a radiator may work if the valve really shuts tight but only if the leak is in the radiator. If the leak is in the pipe from the main to the radiator valve it won't work.



I've seen old steam pipes become porous along their length but elbows and their joints maybe more likely. If the pipes are not insulated you might be able to find a leak by using a cold peace of metal and see if steam condenses on it. This will only work when the air is very dry and the metal, or small mirror, is cold.



Look for signs of stained wood, peeling paint, or warped boards that might indicate a lot of moisture near a pipe.



good luck,



Bob

Jeff_44

Thanks

One thing I did last year was to shut off all the rads while the boiler fired up. I watched the gauge and the pressure registered fine. I shut off the boiler and let the system settle for a minute. I then opened up rad valve and listened as the air vent hissed quite loudly, allowing the air to return - As far as I can tell, this let me know that the system is relatively tight (for being over 70 years old). Am I on the right track here?

BobC

One test begets another

That test just verified you were not condensing steam in the radiators so the system was able to raise pressure. At what point did pressure shut the system down?



One interesting test would be to replace all of your radiator air vents with 1/8" threaded plugs and replace the main vent(s) with the proper size threaded plug or cap. Now all exits for the steam would be closed off; then let the system run for an hour or so. First see how long it takes to reach the pressuretrol cutout setting then see how long it takes the pressure to fall to the cut in setting. Those are good number to know.



If everything was really tight nothing should get hot except the boiler and header and some of the piping close to the boiler (getting hot by conduction in the piping). If something gets hot away from the boiler you must have a path for air to escape that is letting steam into that leg. At least then you will know about where to look for a possible leak. If a main or radiator leader pipe only gets hot halfway down the leak is probably in that general area.



Keep an eye on the boiler during this test to make sure your pressuretrol is working right, I'd shut it down if the pressure gets above 5psi. It should be 2psi or less.



good luck,



Bob