Water heater - hot water disappears

[JackScrap]

3 licensed plumbers later . . .

40 gal natural gas water heater. The heating part is working fine, when the water's cold enough the burner kicks on and heats it.

But! For no reason I can find, the hot water pressure fades away to zero at all the faucets in the house. This has happened several times. Then it comes back full force and works fine for a day or so.

Pressure on the cold water side of the faucets is always fine.

Cold water to the house comes in right at the water heater and spilts. Since the cold water pressure never drops I assume any filling/pressure problems on this side are inside the tank.

Hot water goes out and immediately splits in several directions. Since faucets in all directions stop getting hot water, I again assume an out-flow problem is inside the tank.

Tank has been drained and refilled. Very little sediment or anything except clear hot water came out. Burner kicked on fine and heated the fresh tank of water.

The standard answer I'm getting is "we'll gladly replace your water heater but no guarantee it will solve anything".

I don't think they know what goes on inside a water heater and neither do I.

Anybody?

 

[Verdeboy]

I'm certainly no expert on this, but there is a dip tube in the HW heater that may be plugging up and then unplugging. It's also possible that a chunk of corroded metal or something else blocks and then unblocks the flow of water somewhere else in the system. Here's a link that will show you the inner workings of a gas hot water tank.

http://www.chilipepperapp.com/GWH.htm

 

[Sponsor]

 

[Mikey]

How old is the WH? What brand?

 

[JackScrap]

It's a Rheem natural gas 40 gal water heater (a common old brand here in the SF Bay Area). I believe it was installed about 7 years ago, new.

Something clogging a line elsewhere has been ruled out since:

1. the hot water line out of the heater splits to go two different directions just 12" after leaving the water heater ... and both directions are affected by the problem when it happens.

2. The cold water comes into the house and splits 18" above the water heater with one line going off to the fixtures. The cold water is always full pressure at the fixtures and it appeared to be full pressure when they had the water heater drain open with the cold water supply on.

The lines in and out are all 3/4" copper. There's no leaks anywhere. Oddly enough, it's worked fine all day today after having normal cold water but no hot water pressure for most of yesterday.

 

[Verdeboy]

Did anyone take the inlet and outlet fittings apart to see if they were pluggged? You can do this next time the pressure is low, but you'll probably need two large pipe wrenches -- one as a counter wrench.

I don't think HW tanks last much more than seven years anyway. Might be a good idea to replace it if you can't get this thing solved cheaply.

 

[hj]

water

You have to call a plumber when you do not have hot water, so he can diagnose the problem and where it starts. Your description is illogical, so if it cures itself, the plumber may not be able to cause the problem when he is there, and anything he tries as far as a cure would be a guess shooting in the dark.

 

[Mikey]

When the failure occurs, you could open the WH drain and see what kind of pressure you've got in the WH. This could rule out any problems with the supply or dip tube. A better method would be to attach one of those cheap hose-bib pressure gauges to the WH drain and just monitor the pressure all the time. If the gauge shows pressure in the tank, but there's no pressure at the fixtures, there's a problem somewhere after the dip tube. Can you post a picture of the HW plumbing from the tank to the point where the HW pipes diverge?

 

[Master Plumber Mark]

nipples in the tank

you got some of those galvanized nipples
in the top of your tank that have "check balls"
in them.

These little balls are supposed to hold the heat in the tank but can clog up or jam up..

If that is not the case then the top of the heater
at the nipples are rusting shut

eiither way you need to simply check the top of the water heater for a clog


the last question.......are you on a slab home or on a crawl space???

occasionally we run into a problem with a leaking
hot water line in the slab....


any normal plumber should be able to figure out
this one....

 

[Cass]

A better method would be to attach one of those cheap hose-bib pressure gauges to the WH drain and just monitor the pressure all the time.

Be sure you attatch this only to the drain at the bottom of the heater and not to the temp/pressure relief valve.