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?

Jamie Hall

The answer to how low can it go is... "it depends". On where the low water cut off is set, which varies. Can you either describe yours, or better post a picture of the boiler showing the sight glass and the low water cut off?

If the LWCO is a float type, there should be a drain on the bottom of it. That drain should be opened fairly often -- perhaps as often as once a week -- and allowed to run until it is at least not gunky. Doesn't have to be drinking water clear, and likely won't be. Doing that also should shut off the boiler if it's running -- a useful check.

garimh

Thanks for reply Jamie. I've attached a photo of my low water cut off. When I said I blow down the boiler often (every week or two), it's from that yellow handle so perhaps I'm blowing down the LWCO and not the boiler?

garimh

Just a bit of extra info, I had boiler serviced before firing it up for first time last winter. Guy reduced pressure from about 2.5 to 1 and also said auto-fill had been disabled for some reason and that he was leaving it disabled in case it was faulty. Otherwise, he said it was well maintained.

Photo of LWCO attached.

Fred

That is a MM #67 so what I have said below and in your other post is correct:
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.

garimh

Thanks for that Fred. I'm not sure I'm feeling confident enough to take LWCO apart for cleaning so perhaps will call someone in for that. Does the whole unit need to disconnect from system or does a cover come off while it stays in place allowing me to clean it? It's removing the whole thing from boiler that makes me a bit nervous.

With regards to other comments, the Pressuretrol is definitely set for a cut-in of .5. However, I'm attaching a photo of inside white wheel. The 1 on the wheel is facing outward but I don't see what the number if supposed to line up with to indicate its position. Is that how the wheel is supposed to be sitting in the box?

Lastly (and apologies if this is a really stupid question), I'm assuming my other attached photo is the main vent? If so, I don't see or hear any steam escaping there or at any of the radiators. Had to replace all radiator valves in house last year and I put in Varivalves. One or two ended up failing a second time but all are quiet now and seem to be working fine.

Fred

Yes, the "1" should face out at the front of the Pressuretrol. It looks like it is fine. I like to take my LWCO off of my boiler to clean it but if you take the cover off of the electrical box on the end of the unit, you will find two screws that allow you to take the switch unit off and then there are about 6 screws that allow you to pull the float unit out of the housing. You can then take the 4 screws off of the blowdown valve body and take the blowdown valve off. At that point, if you lay on the floor, you can scrap the inside of the housing out and clean it out. BEFORE YOU DO THAT, HOWEVER, YOU WILL NEED A GASKET KIT (ROUND) THAT GOES ON THE END WHEN YOU PUT THE FLOAT BACK ON AND A GASKET THAT GOES ON THE BLOWDOWN VALVE BEFORE YOU SCREW IT BACK TOGETHER. If you do this yourself, order those gaskets before you take anything apart. I'd be inclined to wait till Spring if you are not familiar with that unit, just so you don't find yourself without heat, if it doesn't go the way you want it too. Or if you have a good Steam Pro, he can do that in probably a half an hour.
Also, that is a Gorton #1 Main vent in your second picture. I doubt that you have enough venting on your main if that's all you have. We typically say one Gorton #2 for every 20 or so feet of 2" main. It takes about 3 Gorton #1's to equal a Gorton # 2.
In any case, that wouldn't cause you to lose water in your boiler but it will cause the steam to be very slow expeling the air out of your mains before the radiators get steam. Essentially wasting fuel during that extended time.
Do look everything over and make ure nothing is leaking and evaporating. It just takes a small leak to cause the kind of water loss you are talking about.

garimh

Just to follow up on above, I found two valves in my home that were a problem. The Varivalve in upstairs bathroom was bubbling and hissing as was a another Varivalve in upstairs bedroom. Strange as both of these has been replaced in past year or so. Bathroom one was definitely clogged when I tried to blow into it so replaced it. The bedroom seemed OK when I took it off but as I had already purchased new valve for it, I put the new on there and for two days all were good and quiet. Now, this morning, the Varivalve in main bedroom is hissing and gurgling. This one was just replaced back in September so something is going on causing these new vents to fair.

It's mentioned above that my main vent is wrong size. Could this be problem? Or perhaps my system has so much crud it in that fragments and sediment are making their way up and ruining these valves?