wierd situation

Hi Mike, A few questions:

1. Is there a hot water return system of any kind?
2. What is the routing of the CW service?
3. Is there any possibility of a cross-apartment cross connection?
4. Have you checked the dip tube?
5. Have you shut down the cold side of the water heater and confirmed that the cw entry is on the right side and that all the hot side openings are dead?

Please answer each question to the best of your ability.

Bob Wheatley

Any chance someone hid an expansion tank on the hot side of the WH and its pushing water back when system pressure drops while a cold faucet is open? (A very WAG, I know...)

Jeff

sounds like a cross connection caused by a bad tempering valve on a toilet or something like that. when givin equal pressure drop hot will fight its way to front of line.

I'd suspect the happy homeowner piped cold to hot under the bathroom. Because of different hot/cold pressure drops in the piping this could work out just as you describe. Water will take the path of least resistance. This could mean that all the hot comes through the water heater undiluted by cold but open a cold faucet and half the water comes backwards through the water heater from the cross connection.

MM

try to isolate the toilet if you can't get to the pipes, otherwise crawl under near toilet and look for tempering valve. id start by looking at all my tempering valves.

Guys,

I'm sure it'll make sense when I finally figure it out. There must be a cross connection somehow-somewhere. There's no laundry, nor tempering valve, nor single handle faucets. It's city water, and not a well, meaning the pressure is consistent and strong. I think the dip tube is OK, since there's sufficient hot water available.

What I find really confusing is that the water is backing through the water heater when running the cold, and yet when the hot is used it's not affected. I'll let you know when I solve it. Thanks for the suggestions.

what about the shower valve isn't it a tempering valve?? last time this happen to be it was a becon valve hidden in floor under toilet.

"Ned Flanders"

The shower valve is a two handle valve, so a cross connection couldn't happen without me knowing it. I also checked the toilet, and I can tell by the layout and visible pipes that there's no tempering valve.

The former owner piped in a new shower and sink. It's probably in there somewhere.

I'm not sure if I'm going to start tearing walls out, or if I'll just put a check valve on the WH.

Shut the cold valve on the water heater and then turn on each hot tap in turn to see if any cold comes through the suspected mystery cross-connection.

MM

"Mark Monson" <

I already did that, and the hot seems normal. See why I'm a little stumped!

is there a washing machine?? it is rare but a stuck solenoid can cause this.

"Ned Flanders"

There's no laundry, which was one of the first things I thought of. I'm pretty sure it's that some moron just connected a cold to a hot when the bathroom was remodeled. The backing through the WH is what's confusing. The reason I'm surprised is that I'd think that when, for example, the cold is turned on in the kitchen, that there'd still be pressure on the cold side of the WH that'd be pushing in opposition to the hot. It's wierd.

draw it out on paper and pretend you have a vacuum cleaner on the end of every supply. follow the easiest path to water heater if you draw a cross connection. remember the hot is going to be higher pressure than the cold so it will go first. The kitchen sink being weird I assume means the sinks cold supply is next to the incoming water which is high pressure. you would think that cold would just zip right out the cold faucet. However at the tee where your water main comes in will have slightly greater pressure on the downstream side pushing back against the water main; so when you turn on the sinks cold it sucks from the downstream side of the tee not the incoming main, which could cause reverse flow in the wh caused by venturi effect. the tee where you have the cross connection becomes the new water main for the cold supply to the house because it is the opening to the cold system with the highest pressure. On city water i install a check valve on the cold supply to wh then a thermal expansion tank.

"Mike Grooms" wrote in message news:d5c72$43281c95$d8c4bafb$ snipped-for-privacy@FUSE.NET...

I assume there's no hot water return system, right? If not, and by turning off the the cold supply to the water heater you only have cold water to the cold side of all the fixtures your problem is almost certainly pressure that is being created by the heating of the water. Your maost practical recourse is to put in a check valve on the cold supply of the heater and an expansion tank on the hot side.

Keep us posted how this turns out.

Bob Wheatley

"Ned Flanders"

Some of us have mentioned that the hot water will have more pressure than the cold. If there's no check valve on the WH, why would this be true. It doesn't make sense to me.

Mike

Just because there's no check valve does not mean that the pressure is not still being created. It just gets pushed back up into the cold side. The hot side is a closed system so it cannot acept "anything" as long as the fixtures are not in use.

Bob Wheatley

expansion tank on cold inlet NOT on hot outlet. check valve right before expansion tank.

the expansion starts there so does the pressure.

Yeah, that was poorly worded. I meant on the "hot water heater" side of the check valve. I should drink a couple of beers before I start typing so my brain don't outrun my fingers...:>)

Bob Wheatley