How low should water level be in indicator before boiler automatically shuts down?

garimh

We moved into a new house last year that has an old steam boiler (not sure how old but it's an HB Smith G210). So, I'm fairly new to steam heat.

Last year I had a problem with leaking radiator vents, etc. which was forcing me to add water to boiler every few days. I thought I had all leaks accounted before this season started for but now with winter here and boiler running often, I find the water level indicator is dropping about an inch or two every few days.

Prior to reading of this site yesterday, I was blowing down until water runs clear after turning off boiler and allowing it to cool. I'm now reading that I should be doing it with boiler on to test low water cut off, which brings me to my question. How low should water in indicator be before the boiler shuts down? Because I had it down to about a half inch of water in glass and it was not turning off. I got a bit nervous at that point so shut if off manually, will let it cool, refill and turn back on but I'm wondering if I needed to keep going to properly test. If not, I'll have to have a pro come in to check it.

As for the refilling, all of my returns are above ground and I have no visible leaks. I'm wondering if perhaps there is a leak in boiler and will look for white smoke from chimney. Any other ideas? Or maybe the amount of water I'm putting is in normal for an old boiler?

BobC

You will have to empty the gauge glass (or very close to empty) to trip the LWCO. I would test it with the boiler cold the first time to be sure it works.

The low water cut off should be cleaned every year. What kind does the boiler use, post a picture if your not sure.

Bob

garimh

Sorry, not sure how this thread got posted twice. I posted photo of LWCO in other thread. Perhaps moderator can delete this one?

Fred

If you have an McDonnell Miller #67 Low water cut-off on that boiler, and you test it while the boiler is running, it should shut the boiler down within about 5 seconds of opening the blow down valve. That is because water can not fill the LWCO as fast as the blowdown valve releases it and the float in the LWCO will trip the switch in LWCO to open the circuit and shut the burner down. Again, assumming the LWCO is a MM #67, in normal operation the float is designed to shut the circuit down when the water level in the sight glass is at the top line designed into the front and/or back side of the body of the float chamber (looks like a decorative pattern in the casting but it is actually the Low water line for this style LWCO), which leaves about 1-1/2" to 2 inches of water in the sight glass.
If it does not shut down the boiler burner when you open the blowdown valve, most likely there is enough buildup on the side walls of the internal float chamber that it prevents the float from free movement. That unit, or any other float type LWCO should be taken apart once a year and cleaned (scraped) out, the float should be checked to make sure it doesn't have a leak in it and the gaskets replaced. The unit should then be tested to make sure it works.
As for leaks, make sure all of your vents (both radiator and Main vents) are not letting steam escape. Make sure your Pressuretrol is set for a Cut-in (front scale) of .5 PSI and the white wheel (inside the cover) is set to "1" to give you a cut-out pressure of 1.5 PSI. Also, once a year, the Pressuretrol should be taken off the Pigtail (looped pipe it is mounted on) and that pigtail taken off and cleaned out. They often get pluged with gunk and the Pressuretrol can't see the actual system pressure. High pressure will cause water to leach out at various places (vents, valves, etc) and that water will most often evaporate before you can find it.

Walk all of your mains and returns in the basement and make sure nothing is leaking there. Small leaks can cause a loss of a gallon or two of water over a few days time.