water heaters

I am aware of three failures of gas water heaters- Tank leaks, buy new heater. Second, thermocouple quits, pilot goes out, water is cold. $8 at the hardware store, new thermocouple, fixed. Third, dip tube on cold water inlet breaks off, water is hot but gets cool, then cold quickly.

My thermostat seems to have too wide a range. If I am home and using hot water through the day, its fine. If I use no hot water for a few hours, it cools off to the point that full hot in my shower is barely comfortable. The thermostat seems to be part of the gas valve, and I can see no limit adjustments.

Any education for me?

If its still under warranty, call the number on the side of the tank and tell them it fluctuates wildly. Sometimes you get up in the morning and its cold, and sometimes steam comes out of the faucet. They will send you a new gas valve and aquastat. If you have to buy said control because the water heater is out of warranty, just buy a new water heater. Replacement is straight forward. Shut off gas, shut off water going into the cold side of the water heater. Crack a hot water faucet until water stops. Close faucet. Undo union in gas line and remove gas piping between union and gas valve. Remove any other lines or wires from the gas valve that go down to the pilot and burner tray. Unscrew gas valve. Water will come out of the hole where the aqua stat screws in, but as long as you relieved the pressure and the faucets are closed, only a quart or so will come out if you insert the new one quick enough. If that scares you, drain the whole water heater down first. Reconnect everything and relight.

If you have an old house with old faucets, they may blow over to the hot side and come out your water heater when you drain it. I shut-off supply to my leaking unit, then drained it. Water kept coming out. Had to shut off water to the house. It was easier to put a ball valve on the hot side then to track down the bad faucet. I've got new gas water heater now!

The old one only lasted 25 years......

Have not had your water heater symptoms so I'm no help.

Have you tried percussive maintenance? Running the knob through it's range? I don't think there's much else you can do besides replace the thermostat.

Just making sure, you dont have a long run from the fixture in question and the water heater? It could need a circulator pump. That might be why if you are using all day it stays warm but if you are gone, all that water in the pipes are cold. Just a thought.

Its almost 20 years old, and its changed its behavior in the last few months. I figure the correct answer involves a new unit. but I just thought I'd ask...

I had the same thing happen to my water heater at the old house. For the life of me I can't remember how we fixed it, but it didn't involve a new heater. One thing I remember doing when troubleshooting is flushing the tank. Hook a hose up to the bib at the bottom, put the outlet of the hose in the tub or toilet, open the valve on the bib and run it for a while. Don't turn off the water feed to the tank - you want fresh water coming in and cycling through.

Once you're done flushing it, be aware that you have a garden hose full of water inside your house. Either keep both ends high while getting it out of the house or have two people on hand to help deal with getting it drained without soaking your carpets or something.

That might have been enough to have fixed it. I'll check with my wife. I think the theory there is that there was some build-up in the tank that was insulating the thermostat.

dculberson wrote: Don't turn off the water feed to the tank - you want fresh water coming in and cycling through.

The other reason to not turn off the water feed to the tank is that your shutoff valve may be ancient and decide to break. Two days ago I noticed the water heater was dripping from the bottom valve, so I thought I'd crack it open to blast out any crud and hopefully reset the seal. I didn't want to get hit with a ton of pressure, so I turned off the supply line. It has a valve like this:

Inside it looks like this:

See that threaded part? Yeah, that broke off right as I bottomed out the valve in the off position. The handle just spins and spins. I had to drain the house water pipes, then open up the valve and remove the broken piece. A cordless impact was required to get the valve apart. I pretty much gutted the valve, so it is decorative now. I'll go buy new guts for it this week, but what a pain. All because I wanted to be cautious.