Why water shooting out of main vent?

bruce_21

End of the line main vent had water shooting up 8" and all over everything. Why? Took all the return piping apart all the way back to the boiler. lots of rust nodules and crud but nothing was completely blocked. Can't get the pressuretrol to shut off at the 1.5 psi it is set at, pressure goes to 3.5 psi on nice 5psi gauge. Pressuretrol was replaced only 2 years ago. Piping system is 50 yrs old+ with newer Burnham V-36. Are there chemicals to desludge this beast?

Steamhead

Is this a one-pipe or two-pipe system?

aircooled81

Is the main vent less than 7 feet high from the condensate return low point?
Maybe water (condensate) backing out or stacking in the return?

nicholas bonham-carter

Pressuretrols will frequently loose their settings, when you try to adjust them down to the needed low pressures of 1.5 psi.
In addition to that a clogged pigtail will prevent the pressuretrol from seeing the pressure, and it will overshoot.
The most reliable thing to have would be a 0-4 psi vaporstat, with a 0-3 psi gauge next to it.
High pressure will cause the water level to rise in the wet return, and if high enough will go above the main vent level.--NBC

BobC

First take the cover off your pressuretrol and make sure the dial is set to 1; the front scale should be set to 0.5. Pressuretrols have almost no quality control so it's the luck of the draw to get one that works right.

Have the pigtail cleaned and if that's not the problem then replace it with the vaporstat as NBC suggested.

Bob

bruce_21

I will check the pigtail on the pressuretrol today and clean or replace it. What about cleaning the boiler's innards? I'm wondering if it surged and got rust or whatever into the pigtail. Are there chemicals to dissolve rust and scale? This is an old system. Will a chemical like Hercules Scout just fill the bottom of the boiler AND the return! with a load of sludge?

BobC

When i had my Smith G8 installed in 2012 I used Steam master tablets to treat the water, that water was still clean yesterday when I drained off a gallon.

With an old boiler a good power flushing might help (do it when the boiler is cold or just warm) , what kind of boiler drain valve do you have? Full port valves are a lot less likely to clog with sediment.

I've never used cleaning chemicals on my boilers so I'll leave that to people more knowledgeable than I am.

Bob