Ok, here's my story:

I moved into a 55-year old house a month ago. It has copper pipes and a 10-year-old 40-gallon lowboy water heater in the crawlspace. The pressure from the city water line is 80psi.

After about a week, I noticed my hot water wasn't staying hot. I called the plumber who came out and replaced the upper thermostat and upper element. This didn't help much, so he came back yesterday and installed a new Whirlpool 40-gallon lowboy. Thankfully, this was all covered by the home warranty. We set both thermostats to 125 degrees.

So this morning I got up and tested the waterat the bathtub, turning the hot on all the way. The plumber had said that my bathtub should fill to the overflow with hot water. The bathtub was slightly more than half-full when the water went cold. This is the same thing that happened with the old water heater.

I called the plumber again, and he said to measure the amount of hot water with a bucket. He said if the water stayed hot for 30 gallons, everything was working properly. My bucket holds 2 gallons, and in total, I got 27 gallons of hot water before the temperature started dropping. By the time I reached 30 gallons, the water was cold. Does that seem like a functioning water heater? By the way, the bathtub is proably about 35 or 40 feet from the water heater. How much would insulating my hot water pipes under the house help?

Also, as I was testing it tonight, I heard a "CLUNK," and the hot water pressure dropped considerably, but only in the bathtub faucet. Our bathtub has the 3 knobs (hot, shower, cold). I pulled the little cap off the hot knob and removed the screw, but the knob didn't come off. Should it just pull off or twist off? From reading in this forum, I'm guessing the plumber knocked some junk loose in the pipes that then ended up somewhere between my bathtub and the rest of the system. Should I try to disassemble the faucet and drain it? The cold water pressure is still fine, and it seems like the shower pressure is OK, so do I just need to work on the hot knob?

Thanks for any and all advice.
Steve.

Good morning Steve,

You have pretty much analyzed your problem of the hot water pressure loss.
Your plumber disturbed some crud and now it's clogging the hot water seat of your bath faucet. You could call him back or if you wish you can shut the hot water off at the heater and tear into the valve yourself. The knob pulls off and you'll have to disassemble the valve, pull the stem and washer assembly, clean out and crud and then, before you reassemble the valve, turn on the hot water to,flush out the supply. As for your old water heater before I sold you a new one I would have replaced the bottom element. When you run short of hot water that's the one that usually goes bad. If the top element goes bad the water's cool from the gitgo and it's seldom I've ever found a faulty thermostat that needed replacement. Good luck, Tom

Hi,
The post from speedball is very, very informative and good.
You might also consider "flushing out" your water heater. If you haven't done this for awhile, turn off the electricity at the circuit breakers. Hook up a water hose to the bottom of the water heater, and let all the water drain out, letting fresh cold water come into the heater at the same time.
If there is residue that has broken loose from the heating tubes in the heater, it will be flushed out. Let the hose continue draining until the water is cold, and then let it continue draining for many 5 more minutes.

Fred,

I appreciate the input but Steve has a brand new water heater. However, your advice is very timely for any one that has a older heater with the same symptoms. Thanks again, Tom

speedball1 and fredg, thank you so much for your help.

I removed the screw from the end of the hot knob, and although I wasn't able to pull the knob off the stem, I was able to slide the flange back enough to get a wrench in there to remove the fixture. I went under the house and turned the hot water back on, went inside to look, and then I ran like crazy back outside to turn it off when I realized water was spraying all over my walls! I had no idea the water would come out with such force! Anyhow, I went back inside and found that the water had forced out a little black rubber thing. The plumber had pointed it out before he installed the new water heater. It's a little black gasket or valve or something that fits down into the water heater pipe. He said it's got something to do with preventing heat from escaping from the water heater back into the cold pipe. Something like that. He also said that they can be damaged by heat if the installer holds a torch on the pipe for too long while making the connection. This one looked somewhat melted, so I assume it came off while he was soldering and found its way to my bathtub. My water pressure is very good now! Thanks for your advice.

I also insulated the hot water pipes tonight so that I may have more hot water in the bathroom now.

Also, like I said, I couldn't remove the knob, even after I took out the screw. I pulled and pulled and even covered it with WD-40. I'd really like to remove it because I messed up the flange trying to removing the fixture. I bought a new flange at Lowe's, but I can't install it because the handle won't come off. Are we sure this handle should come off? I can't find a brand name on the faucet or handles. It seems like it should pop right off, but maybe it's corroded. Any tips for removing the handle?

Thanks again for everything.
Steve.

I have learned from Tom's previous posts that they actually make a tool to remove the knobs. On the other hand, go buy a matching pair of new knobs. Likely you already have a hammer. Smash the sucker, along with the one on the other side. Put the new knobs on.

Good morning Steve,
Labman was correct when he said; " I have learned from Tom's previous posts that they actually make a tool to remove the knobs."

It works just like a wheel puller and all plumbing supply houses carry them.
Good luck, Tom