Crossed Hot Cold Pipe?

JEMM55

Hello Everyone

I have a 2 pipe steam system in a 5 story brownstone.

I am having two issues and although I have read everything possible about steam Dead(thanks Dan) and alive I am still in a quandry. Most of the contractors I have been dealing with are pretty much lost when it comes to the real nitty gritty of these systems.

Little by little I am putting in new stops on the toilet supplies and changing out the stops under the bathroom sinks that are real old and not holding. Anyway...when I shut off the main water supply to the building, the toilet tanks back up with hot water. Somehow the hot water is backing up into the cold side of the system. In order to stop this and be able to change the stop without a flood of scalding hot water, I have to drain down the boiler and leave it open. Bizarre, though I valve it closed, it seems to continue. One of my licensed plumber pals says it is because the water is crossing over at a bad shower diverter. I have three knob shower bodies(hot, cold & diverter). Does this make sense and if I change the diverters will I get control back of the system?

I personally think there has to be a bad backflow on the system. Your help is appreciated.

I will post my second problem in another thread as it is strictly a steam discussion.

Alan

nicholas bonham-carter

hot water where it shouldn't be

do you have your hot water produced by the boiler?

the key may be in your description:

"when I shut off the main water supply to the building, the toilet tanks back up with hot water"

this sounds like a cross-connection between some sort of expansion tank [on a hot water loop?] and the hot water-boiler circuit, maybe due to a bad hot water heating coil when the main stop valve is closed, there should be no residual pressure left in the potable water system.--nbc.

JEMM55

crossed pipe

The boiler produces steam and also has two tankless water heaters as well.

The coils on these heaters were changed a year ago when this question first arose.

Not likely a bad heating coil.

There is no expansion tank and the hot water loop looks fine from the boiler room.

JEMM55

My Boiler

A pic of the upfront on my system

JEMM55

My Boiler

A pic of the upfront on my system

MikeL_2

variables

Jemm55: If you start an orderly process to identify & eliminate any / all possible contributors to the hot water migration you will discover the source; are you sure of the integrity of the valves on the inlet & outlet of the domestic coils. Is there a range boiler or another type of domestic hot water storage tank? Could one of the shower valve handle sets be left open / on with a shut off at the fixed or hand - held shower head? If your domestic hot water coils are not isolated from the loop, the hot water from the higher floors will back feed through the coils into the cold water piping .........................

JK_3

Mixing valve ?

There are a few different things that could be causing this. Some of the first that I would check would be a bad mixing valve or any single handle faucets . There would be a process for checking to see where the hot is coming from when the main is shut off. Does the hot just start feeding to your toilet tanks when the main is shut off or is it when you attempt to drain the tank? Does this happen on any or all floors or only the lowest floor ? If you would like to give me a call I can try to help you on the phone . I do a lot of work in the old brownstones in Brooklyn and am very familiar with the systems. 

Jamie Hall

See if I can get this clear...

You shut off the main valve to the house.  This eliminates (we hope) street pressure from reaching into the house.



You have no expansion tanks or hot water heating loops.



You do have two tankless water heaters on the boiler -- but if this is a steam system, the pressure on the boiler side is essentially zip, so water won't go from the boiler into the hot water system, at least it won't go any higher than the water level in the boiler.



You say that to get the flood of hot water to stop you have to drain the boiler.



Which leads to the question: is this stop you're working on below the water line in the boiler? 



If so, you do indeed have some kind of cross connection between the boiler and your domestic water, and you need to find it and eliminate it (it could be a leaking valve in the boiler feed, although that seems unlikely as you would notice the boiler water level rising -- and if it's a flood, rising rather quickly.  Ditto if there were a leak in one of the tankless coils).



I can't think what it would be; without being there and tracing out the pipes.



On the other hand, if this stop is above the water level in the boiler, it's not boiler water.  What it is I can't say -- but somewhere you have a volume of hot water which can flow back through the cold pipes to your stop.



So... pipe tracing time.

kev

water

is most likely seeking its own level through that tempering valve I see in the photo.  Close the cold water to tempering valve. draining the boiler may seem like the solution, but in fact is not. Hope this helps.

icesailor

All Wrong::

Guys,

If the steam boiler is running and making steam, and the domestic hot water coils are submerged in the 212 degree water in the steam boiler, and you remove the pressure in the potable water, the hot water in the coil will turn to steam and push the hot water out of the coil by compressed steam.

Haven't any of you disconnected a tankless from the potable water system to work on it and have blasts of hot water come flooding out of the pipes? The steam bubbles don't care where they go.

I've seen water in a tankless coil start banging when I drained the water in a house and the water in the boiler was very hot.

If everything was charged up and you were getting hot water out of a cold water faucet, you have a cross connection somewhere. That's another issue. Finding a cross connection is an art form that is developed from experience.

Tim_Hodgson

With out an expansion tank

is it possible the indirect coils are heating the domestic water and creating excessive pressure in the hot water lines as the water expands?



Tim

JEMM55

Now there is a thought!!

I am going through all of the possibilities. I will keep you informed

Jamie Hall

Good call...

hadn't thought of that, although it's happened to me.  Stupid me (there are times I shouldn't be turned loose).

icesailor

Pressure:

That's what I said in my previous post.

You have valves leaking bye. The main shut-off could be leaking bye.

In my long career of doing this stuff, if you are in a multi-story building, and you have shut off the water to the whole building, you open the faucets on the floor below where you are working. Water seeks its own level. If you open the faucets below, the overflow will drain out below. If the boiler is hot, the potable water will boil in the coil. The rising steam bubble will push the water out wherever it can.

Trust me. You do not have a leaking steam coil. It leaks both ways. If you turn on the water to the system and the boiler floods, you have a leaking coil. If you have a leaking coil and you turn the potable water off, there isn't enough pressure in the system to push the water up to any height. But expanding steam in the potable side of the coil will make it push up and overflow out of an open pipe. Ask me how I know.

That's why at this stage in my life, if I have to get into a potable water system, I blow the entire system out with compressed air. If I have to solder something and water shows up, I'm screwed. If something starts running out of a pipe, I'm alone, and I'm screwed with water running all over a floor just waiting to find a way to a ceiling below.

If you are working on the second floor, and you shut the water off in the cellar, and don't open the faucets on all the fixtures above and below you, the fixtures above will leak down. Every time.

If the potable water system had no problems before you drained it, and it is OK when you turn it back on, there's nothing wrong. 

JEMM55

Mixing Valve

This is a two pipe steam system that I inherited with lots of previous fixes.

I have been addrressing the problems in a logical way.



On e at a time such as, changing all the steam traps on the radiators that had been there for twenty years.



I am removing air vents from radiators  on this system.  ( Some genius decided to fix things by adding air vents randomly around the buildings radiators.)



We are trying to figure out why there is a cross over with the hot water...it rushes back to the toilet tanks when we turn off the main supply and flush the tank to drain it.



We have a random on and off problem with the slow returns and overfilling of the boiler.  We are thinking of changing our current water feeder to a VXT.



I would be very interested in meeting with you at a mutually convenient time to discuss the heating and plumbing needs of all of our buildings.



Alan

JEMM55

Opening the faucets

I always open the faucets above and I too always try to make sure that there is no water in the system.  As you say...not pleasant to try and solder pipes that are wet.



I manage two other buildings with steam systems and neither one has this issue.  When I shut off the main to the building, there is no more water anywhere hot or cold.  I then open a faucet in the basement and the whole system drains ...thereby leaving me with a dry system to sweat to my hearts content.



Only this one building has this weird issue.  I have tried just about everything and cannot figure out why the hot water backfeeds through the cold lines.

icesailor

Hot Water:

If you shut off the main water service valve, and open the faucets in the cellar. and open all the faucets in the above floors, there is absolutely no way that water can migrate UPSTAIRS from the basement.

If it is, there is something wrong that needs to be found and addressed. If you shut off the main valve to the building, and there is no other source of pressurized water into the building, it is physically impossible for what you describe to happen, Either you missed something or there is another live feed into the building.

Is the water meter inside the building or outside? If inside, is the small wheel moving when the valves are off? Look. It shouldn't be moving. Does the building have buildings on either side? Could there be a pipe from one other building feeding this building? Do you have an automatic fire protection system in the building?

Post a picture of the water service and meter coming into the building.