Strange Plumbing Problem

[Eric F.]

I bought a condo three years ago. In January of this year, my water system stopped producing hot water adequately. I first noticed it from the shower. Then gradually from the remaining faucets in my unit. At first, the hot water would last about 10 to 15 minutes before running out. After about a week, I noticed a leak and called a plumber. The plumber said water was leaking from the water heater's tank, which was the source of the leak. Soon after, after getting two more opinions, I had the water heater replaced. The company that replaced it said the water temperature would return to normal after 2-3 hours. However, the water never returned to normal. After a about a week, I called another plumber to inspect the water heater and test the water. They suggested that something else could be drawing water from the piping in my unit. They said it is common in condos and apartments to see plumbing being shared by multiple units, and there could a leak somewhere else, or water was being siphoned off to another unit somewhere between the water heater and the faucets. I called my water company, and they came out to inspect the lines. They came out three times and shut off the water from the street. During each visit, I noticed a drastic improvement in the water flow throughout the unit. However, after each visit, water flow and the water temperature would gradually decrease, after varying amounts of time, ranging from 6 hours to only 30 minutes. Recently, I started shutting off the main water valve when I am not using water. After the valve is turned off, water will begin to flow into the water heater's tank, and the water heater immediately starts heating water. During this time, the water heater will shut off for a while and then start again. When I hear the water heater start a second or third time, I will turn on one of the faucets. And frequently, I see water running even when the main water shut off valve has been turned off. Mainly from the tub\shower faucet, hot or cold water will run naturally and gradually decrease to a pencil-thin stream, without a decrease in temperature, even after 1-2 hours. Occasionally, but not as frequently as the tub, I notice this from the faucet in the kitchen and bathroom sink.

What could the problem be? Where is the water coming from when the main shut off valve has been turned off? If the water is coming from the tank? If that is the case, then why doesn't it happen occasionally and not all the time? I assume, the water heater's tank still contains water even after the main water shut off valve has been turned off.

 

[breplum]

Yes, of course the tank has water in it even when the main is shut off.
But, turning off the cold water supply at a water heater will stop pressure flow of hot water. After the valve is shut at the water heater, usually hardly any residual hot water flows because it is under a vacuum if you try to open a hot tap.
We would need to see pictures and a piping layout to just begin thinking about what is going on.
It all sounds very screwy. Sorry but you need a smart plumber at this point and not a bunch of guesses from the peanut gallery.
If it was me, I would start by adding a valve on the hot water side of the water heater.
There are all sorts of back and forth testing techniques (all based on logical projection) to see if there might be cross connection. And certainly no water should flow (except residual dribble) when main is shut.
Keep us posted.

 

[Jeff Handy]

I worked on plumbing for a dental office next to a bank.
Neither one could get their hot or cold to turn off completely, and hot was lukewarm, as was cold.

The plumbing had been butchered so many times as tenants came and went.

I removed about twenty or thirty feet of bizarre kludged piping, and cross connections, after hours with both tenants main water off.

You probably have this similar situation going on.

This client even had some heating ducts and electrical circuits that were randomly shared between storefronts.

 

[Jeff Handy]

My first apartment had an adjoining laundry room, shared by four units.
I was convinced I was supplying water and conditioned air to the laundry area.

Because my water pressure dropped, showers got cold too fast, when laundry was being done.
And my a/c settings directly controlled the laundry air temp.

It took me turning off my hot water and a/c before the management finally admitted it.

Apparently, years before, my unit had been given a rent allowance to cover it, but “oh they forgot about it” over the years.

 

[Eric F.]

Yes, of course the tank has water in it even when the main is shut off.
But, turning off the cold water supply at a water heater will stop pressure flow of hot water. After the valve is shut at the water heater, usually hardly any residual hot water flows because it is under a vacuum if you try to open a hot tap.
We would need to see pictures and a piping layout to just begin thinking about what is going on.
It all sounds very screwy. Sorry but you need a smart plumber at this point and not a bunch of guesses from the peanut gallery.
If it was me, I would start by adding a valve on the hot water side of the water heater.
There are all sorts of back and forth testing techniques (all based on logical projection) to see if there might be cross connection. And certainly no water should flow (except residual dribble) when main is shut.
Keep us posted.

The shut off valves on the tank are red. The cold water valve is located on the right, hot water valve on the left. Right now, the main water valve is turned off and the shower's hot water faucet has been turned on for the last 10 - 15 minutes. Water is flowing to the shower normally without a decrease in pressure. And the remaining hot water faucets have been turned on, but they don't appear to be receiving any water through the piping, like the shower.

 

[breplum]

That piping is normal (though the expansion tank should be properly supported with a strap).
Based on your description, you have cross/mis connections elsewhere such that that one particular shower is connected to someone else's supply.
It is a matter of sleuthing other units, like Jeff H said.
HOA likely needs to be involved.