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Tanklets > Cross Connections

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Q: Is there some sort of valve that prevents hot water from migrating back into the cold water supply line. At the closest tap to the water heater, we will ofter get hot water from the cold water tap for about 2 minutes, before the cold water starts flowing. I have checked the cold water supply to the tank, and have often found that it is very hot. Is there a valve that is leaking or a valve I can install to prevent this situation?

A: Two different avenues come to mind. Heat traps are the first measure. Their purpose is to prevent hot water getting into the pipes by convection. They can either be bought in the form of short pipe nipples with a flap inside, or they can be made from long flex connectors. In any event, don't use the type that has a small "marble" inside as it can rattle.

You'll find more info on heat traps elsewhere on this site. The other thought is that there might be a cross connection. This could allow hot water to leak into the cold lines. Check for it by shutting off the water supply to the heater, (only briefly for this test) and opening only a hot tap. It should run only a few seconds and then stop. If it keeps running, cold water is likely getting into the hot side and you need to find out where. In no event should you simply put a check valve on the cold inlet to the heater. Hope that helps. -- Larry (7/12/2006)

Q: For the past few weeks every cold water tap in my house instantly begins with hot water, then it becomes cold. Nothing has been changed on the hot water heater. Does this mean the hot water heater is going out?

A: Hello: Do you have an instand hot water, or recirculating system?

Q1: I don't have an instant hot water. I don't know what the other is. I only have a 40-50 gal gas hot water tank. This problem just started one day. Hot water also comes out the hose and then turns cold.

A1: Hello: Hot water is getting into the cold lines, as you know. One cause for this is a recirculating system, (sometimes called an instant hot water system) pushing hot water into the cold side through a cross connection. So, I was asking if you have that system. It usually involves having a small pump, close to the heater. It circulates water through the hot piping, keeping it hot, ready for use. Whether you have that system or not, three other questions come to mind. Has the water been excessively hot? Do you have any Moen or Grohe faucets? Has any plumbing work been done recently, or anything dealing with a clothes washer? The answer will arrive.

Q2: I am not sure about the instant hot water system, I don't think I have it but I went out and looked at the hot water heater. There are 2 pipes attached to the top of the tank. There is the gas line going in at the side with with temp control. Then there is a pipe that comes up along the side and goes into the tank at the top side. It has a dial that says" relief valve. I don't see anything that looks like a pump. I have thought the hot water seemed a bit hotter. There has been no plumbing work done anywhere in the house or any work to the washing machine. All of my faucets are Price Pfister. I hope this information might narrow it down. Thanks so much.

A2: Hello: Your answers tell me what it isn't, now we need to find out what and where it is. There is a test to find the cross connections. It's detailed in "Tanklets", but basically, water is turned off to the heater and a hot tap is opened. If the water runs a few seconds and stops, there is no cross connection. If it runs freely, there is a cross connection big enough to notice :shock: If you find there is a cross connection, go around to every tap and listen. You should hear water running. Where lines are exposed; like under sinks, you should feel the hot side getting rather cold. Let us know what happens.

Q3: Sorry for my lack of knowledge, but I am not sure on how to shut off the hot water. I went out and looked at the water tank. Of the two pipes on the top, one feels hot, the other cold. The one that feels cold has a lever that appears to be the shut off. Is this it? Thanks,

Q4: Okay, I've done the test. This is what happened. The two faucets in the kids bathroon had a slow drizzle of hot water. The tub in the master bath had a slow drizzle of cold water. However, when I ran the tub hot water I could hear the sound of water in the shower stall. There was that humming sound like when someone is taking a shower. When I would turn off the tub the sound would stop shortly thereafter. I didn't hear this sound anywhere else in the house. The kitchen sink had a slow drizzle. Thanks also for the tip to look up the terms. It was very informative. Thanks again for your help wih this problem.

A3: So, there is a possibility of a cross connection in the shower. A slow drizzle doesn't sound like the wide open cross connection that would be easy to point at as the fault. Anyway, lacking any other culprits, it might be time to replace the seals in the shower valve and see if it does the thing :cool: Do turn the water off first!

Q5: Thank you for all your help. This was rather fun playing detective. It isn't the water heater after all. I was honestly ready to go out and buy a new one when I started searching the web for products and discovered your web site. One less water tank has ended up in landfills. I will now study up on this new shower subject. -- Larry (2/29/2008)

Q: Could it simply be something with the gas hot water heater and not my pipes. The water pressure is fine. It's just you have to let the hot water run forever before it gets even remotely warm. And I mean a long time. I turn the shower on, then make the bed, start the kettle and wake my daughter up before going back to see if there is hot water.

Hate to waste all that water living in a drought prone area. Any ideas? Also, wanted to add that if someone flushes the toilet (even in the other bathroom), the cold water cuts out in the shower and the person in the shower gets a nasty (scolding hot) surprise.

A: Hello: A cross connection is a possibility. Here is a bit I've lifted from another talk, which tells how to deal with cross connections. THE TEST: Turn off power to your electric heater or turn to the pilot position if gas. Shut off the cold water supply to the heater. Open a hot tap. Water should run only a few seconds and then stop. If it keeps running, the shut off valve doesn't work, or there is a cross connection.

Have a look at the shut off valve. Is the pipe between that valve and the heater cold? If so, water is likely leaking through the valve. You also should hear water movement. Replace the valve and try the cross connection test again. If there is no water running from a hot tap this time, good. If it runs, go around the house with your ears on. Can you hear running water?

Try shutting off stops under sinks or at washing machine; until you hear the water stop or see no more running from that tap. Say you've isolated a single lever bathroom faucet as the cause. Personally, I've seen this with older Moen and Grohe faucets. Note that there may be more than one leaking. I've had up to four at once. Newer models may be better, don't know. Clothes washers are supposed to be a big source of cross connection, along with showers (which seldom have shut off valves). Another thing you have that could use a look is the shower valve. I'd consider replacing it with a pressure balanced valve to prevent the rapid temperature change. -- Larry (9/6/2007)

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