Boiler runs dry, then floods

MarkReynolds1

Hi all; Trying to help an elderly friend with a knucklehead repair person.
1500 or so sq.ft. home with a one pipe steam system from the early 50's. Crown 150K BTU boiler, with (yes I know) copper near boiler piping. No evidence of leaks or problems, Hoffman radiator valves appear kind of new,
The system worked well until recently when the automatic fill valve failed and was replaced; it had been leaking and flooding the boiler.
Repair installed a VXT24 automatic feeder, I am unfamiliar with this unit; prefer McDonnell Miller 101's.
The homeowner likes to turn down the thermostat at night about 4 degrees. When she turns up the heat in the morning, the boiler runs about 20 minutes, and the sight glass water level goes to zero and the boiler shuts off. After 10 minutes, the auto feeder refills the boiler and it kicks back on, but by the time two or three cycles occur and the temperature is back to normal the sight glass water is over the top and the boiler is flooding.
This did not occur with the old auto-fill prior to it failing (so I'm told).
I watched a complete cycle. The water level starts normally, but after 20 or so minutes firing the sight glass is empty. If you stop the auto-fill, after maybe an hour the water level will be back to normal.
Excepting the copper piping, I don't see much odd, except for an added drain, to crutch a sag in one of the main lines, This is the smaller piping on the left of the boiler in the attached photos.
The homeowner blames the auto-feeder, but I don't understand why the boiler empties out in a 20 minute firing cycle. Also, not sure why a normal firing can't bring the house up 4 degrees in one cycle on a 40 degree day.



Any suggestions I can give my friend is appreciated.
Mark

nicholas bonham-carter

Maybe overpressure pushing the water out into the wet returns-clogged pigtail, with bad main venting not allowing the air out, and steam in, for such a long time.
Valve off the auto feed and watch a cycle. My guess is the water will return as soon as the pressure goes down. Maybe the wet returns need flushing as well.--NBC

BobC

I agree it sounds like there is a blockage in either the pigtail or the return that is slowing down the condensate return and perhaps some of both?

Sit and watch a boiler heating cycle and see if the pressure gauge needle moves. Since the pressuretrol and gauge are on separate tappings a blocked pigtail won't affect the gauge. If it does move how high does it get? Do the radiator air valves hiss louder than they used to, if they do it could indicate your running at higher pressure.

If that seems to be working I would look at the returns to see if there is a blockage. I believe tghere are switches inside the VXT that let you delay the addition of water and limit the amount you feed. Those may help but they won't fix a partially blocked return problem.

Bob

Jamie Hall

@MarkReynolds1 -- from your description, it sounds like you already have the VXT on maximum delay (you say it takes 10 minutes for it to kick in and fill the boiler). But let's consider the implications of that: the VXT feeds at most a couple of gallons when it kicks in. That means that in 10 minutes, you are getting less than 2 gallons of water coming back from the wet returns. That's not a whole lot more water than you'd get from a dripping faucet -- and means that somewhere in the wet return system there is a near total blockage. Not surprising, they will do that, and wet returns do need to be cleaned out from time to time.

So the first thing to do (besides the real easy stuff, like checking that the pressure is OK) is to completely flush out the wet returns. This may take some doing, depending on how nice the folks were who installed the system. Sometimes there are handy valves and plugged T's which you can use to get at the pipes and flush them. Sometimes... not. Which is a bore. But you do need to be able to really run water through them.

MarkReynolds1

Thanks for the suggestions.
To add, the Pressuretrol is set at the lowest setting. There are three main runs, only one has a vent and and it is one of the smaller Hoffmans so I will get her to replace that and figure out how to add more venting on the others, though the radiators were mostly heated all the way across after the 20 minute firing cycle.
Thanks.
Mark

Fred

When was the new piping done to add a drip/drain to that sagging Main? What you describe to me sounds like a boiler that needs a good skimming. It sounds like there are oils sitting on top of the water that were probably introduced when the drip piping was added. That oil will stay on the surface of the water making it very difficult for steam bubbles to break through the surface of the water. That will cause water to be pushed out into the return piping. When the boiler shuts down, that water will return and any water the auto water feeder has added will make the boiler over fill.
Is there a skim port on that boiler? It must be above the boiler water line to do a proper, slow skim.