Boiler flooding

SteveTL

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?

Youngplumber

It seems to me there must be an obstruction on the outlet of your feed tank. Everyone is going to ask for pictures. Pictures good enough to see your whole setup.

Is the feed tank vented? 

Jamie Hall

How, exactly, is that receiver tank and makeup water controlled? There are really only two options: a boiler feed pump, controlled by a low water sensor (may be combined with one of the low water cutoffs) in the boiler, or a condensate return pump, controlled by a float in the condensate receiver. There is only one valid option for makeup water (anything else will cause trouble): the makeup water is controlled by a float in the condensate receiver.

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...

EBEBRATT-Ed

Could be vacuum in the system holding up condensate if one of the zone valve is closed. Maybe you can run the system temporally with both zones open see what happens

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

JUGHNE

If you have tested the LWCO's and have absolute faith in them, you could shut off the CW supply to the feeder pump and see if the flooding continues.

Is there an electric solenoid valve on the feed line to the boiler?

SteveTL

Boiler and tank are both flooding, feed tank pump is controlled by a separate lwco that is for pump only. Did shut off feed to tank in the past and system didn’t flood and was told it only went off on low water once in 3 weeks. Only other water feed goes into return piping of boiler. It isn’t leaking as pipe has been cut and valve checked. There is no solenoid valve on water line.

SteveTL

Also feed tank does have a vent, steam is not coming out when boiler is running normally, it has a prv feeding tank float.

Youngplumber

Pictures are still in order here. The whole shabang. 

SteveTL

Youngplumber

Wow, now that's some stuff. @Jamie Hall can tell you, but to me I don't know how anything can return down such small piping without it being at atmospheric pressure. Which in my mind means that you need vaccum breakers on the outlet side of those traps. But you have also said that the system worked until recently.

I don't mind being wrong here and am happy to learn from anyone who can interpret these pictures in a better way. 

Jamie Hall

The tank does have an overflow? I couldn't pick it out in the pictures.

The obvious comment is to check all those F&Ts and their strainers -- which should keep you busy for a while -- but which I doubt will prove much.

To @Youngplumber -- once steam is condensed, it's amazing how much steam piping you can compress into a small pipe!

EBEBRATT-Ed

Looks like a Shipco boiler feed system pump on each end.

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.

SteveTL

@EBEBRATT-Ed tank feed has its own meter and seems to be working. Do not see it running when water level is about a third of tank.

Youngplumber

@EBEBRATT-Ed I'm picturing big glugs of return water coming from the returns ununiformly flooding the condensate reciever at times. Does this make sense?

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. 

EBEBRATT-Ed

@Youngplumber
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

SteveTL

150 is working normally when I’m there watching system run.

clammy

Just noticing all the uninsulated piping ,possibly the boiler is going into vacuumed and pulling water out of the tank into the boiler . I would check that check valve on the pump and possibly add a second check where the feed discharges into the boiler . I think a compound gauge w a vacuume scale be installed to see if vacuumed is being formed if so it’s siphoning water out of the tank . Install a vacuumed breaker on your boiler piping also make sure that the receiver tank is vented properly and the vent Is clear not clogged. Is the boiler cycled on a thermostat or is it set up to maintain pressure . Peace and good luck clammy

SteveTL

Boiler cycles on by thermostats, and tank vent is clear. It is where water is coming out when it overflows.

clammy

Do u have a vacuumed gauge or compound gauge installed so u can see if your going into vacuume? If so install a vacuume breaker on the boiler the boiler could be going into vacuume on the off cycle and sucking water past the feed pump check valves . I would shut off the water feed to ensure that it’s not the float sticking or feeder by passing .also check all f n t traps and ensure all are working properly both in venting and in discharging condensate .any issue w venting air through the mains ? If so possibly add a radiator trap above your f n t and tie into the condensate receiver this will help vent air out quicker leaving the f n t to just handle condensate while the trap increases your venting capacity ,it’s a old timer trick I see every decade or so and it works . Peace and good luck clammy

Pumpguy

I think @clammy is on to something with his thought about vacuum forming in the boiler and steam header.

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.