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Boiler flooding

I’m working on a two pipe steam system, boiler is approx. 1,000,000 btu. System has a receiver tank and all returns and end of supplies have traps. Boiler is 7 yrs old, this yrs it started flooding and filling and overflowing tank. System fills through tank and float valve seems to be ok, also has a by pass but know that isn’t leaking. System also has two zone valves. What could cause this to happening this season?
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Comments
Is the feed tank vented?
And -- which is it? Does the boiler overfill, or does the condensate receiver overfill?
Is there any other water connection to the boiler, like a tankless coil?
With that we can narrow it down pretty closely...
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.
Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
Condensate receivers are supposed to have an overflow tapping and a vent tapping. The vent is usually run up to the ceiling above the boiler water line and the overflow is down by the tank.
If the overflow is not there the receiver can fill up with water above the boiler water line and gravity feed into the boiler.
Could have a plugged slow return somewhere.
Bypass in MU water to tank or float valve in tank. Check the city water pressure. The float valves are usually good for 50 psi or so. If you have more than that you made need a PRV if the float valve leaks by.
Also, what pressure are you running? Do you get any steam out of the overflow? Bad traps can cause all kinds of return issues
Is there an electric solenoid valve on the feed line to the boiler?
I don't mind being wrong here and am happy to learn from anyone who can interpret these pictures in a better way.
The obvious comment is to check all those F&Ts and their strainers -- which should keep you busy for a while
To @Youngplumber -- once steam is condensed, it's amazing how much steam piping you can compress into a small pipe!
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.
Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
There are check valves in the boiler feed line as there should be.
So if you are positive you cut the boiler make up water and checked that valve we can cross that off the list.
I would suspect the float control on the feed tank is leaking by.
I forgot what Shipco uses Mcdonnell Miller 21?
But that doesn't matter.
I don't see an overflow in the picture. If you over fill the feed tank the water will go up the vent high enough to open the check valve in the boiler feed line and overfill the boiler by gravity.
Like the returns are airlocked or blocked until enough water piles up, then blam its all in the recieve and boiler shortly thereafter.
You can correct me if that doesn't make sense.
I mentioned something similar in my first post. Zone valves can cause some strange issues.
Not sure but I think the OP is saying that this system has een in for 7 years and they just started having issues.
His first post says "flooding &filling and overflowing tank" We need more information.
It's possible the #150 pump control is sticking and causing the feed pump to run when the boiler doesn't need water overfilling the boiler. Then the boiler steams down to a normal water level and now extra water out in the system finally comes back and floods feed tank and overflows.
I have had several issues with the 150 sticking even when clean.
If you catch that happening change the head assembly
NJ Master HVAC Lic.
Mahwah, NJ
Specializing in steam and hydronic heating
NJ Master HVAC Lic.
Mahwah, NJ
Specializing in steam and hydronic heating
First of all, are you sure you have equalizer lines installed between the header and return line, and also downstream from each zone valve? If not, the condensing steam will create a vacuum in this space which will hold up condensate and prevent it draining back to the BF tank. The BF pump continues to feed the boiler but then runs low and takes on make up water. Eventually the system becomes flooded with too much water causing the flooded condition you describe.
Another thing to consider is when steam condenses in the boiler and header, an induced vacuum occurs. This vacuum pulls feed water from the BF tank and floods the boiler. Another more correct way to describe this is, the BF tank is vented to atmosphere, and atmospheric pressure pushes water from the BF tank up into the boiler, which is now at a lower pressure than atmosphere. Remember: ALL FLUIDS FLOW FROM HIGH PRESSURE TO LOW PRESSURE, ALWAYS.
One sure way to prevent this vacuum from causing water from the vented BF tank being pushed up into the boiler is to fit positive closing valves on the discharge of the BF pumps. These valves should be wired to the boiler low water controls, same as the BF pumps. With this arrangement, water can't flow from the BF tank except when the boiler is calling for water. A simple check valve will not do the job.
Website: www.nashjenningspumps.com
The first step in solving any problem is TO IDENTIFY THE PROBLEM.