I just installed a new A.O. Smith 50-gallon hot water heater. It works great everywhere besides the upstairs shower. There are 2 problems there:
1) Unless I set the temperature on the heater to "B" (which causes the water in the sink to get to 135 degrees) the shower doesn't get any hotter than lukewarm.
2) When it is set to "B", the shower gets hot enough, but turns cold after about 10-15 minutes.

I had the plumber who installed the heater come back. He said that the first thing to do is to change our shower nozzle, because it's letting out too much water (which is true, as we foolishly had another plumber remove the "water-saving" piece last year to get more pressure). He also said that we have a very old American Standard valve and he would recommend replacing it.

The part I'm confused about is if this would solve problem #1 above. Could it be that a defective valve would cause the water not to get hot enough, but when we raise the temperature high enough on the water heater, then it does get hot?

I am not looking for a way to do this myself, just for some advice as to whether I should in fact replace the valve itself, which would be quite expensive.

Thanks for your help!

Tell us more about the shower valve, is it one handle or two? A picture or barnd name might be helpful.

It's one handle. You turn it a little and it's cold, keep on turning and it gets hotter. There's no brand name written on it, but when the plumber saw it I think he said "oh, a really old American Standard valve."

Does that help at all?

Thanks!

Bump

Did your plumber check the hot limit stop? This regulates the amount of hot water that is mixed to the shower head to prevent scalding. If it is malfunctioning or set too low, you will only get lukewarm water coming out of the tub/shower.

Where would I find a hot limit stop? My valve is so old, did they even have this stuff years ago?

Yes the single handle types did have a limit stop when they first came out. If you remove the handle, then the cover plate, you should see a small set screw somewhere next to the valve shaft. Screwing it in/out changes how far you can turn the lever towards 'HOT'. Adjust it so you can dial in more hot water. Be careful how much hot water you allow to mix in; you can be scalded.

Hello Slipskid,

Can you please give me a reference of this valve you are talking about, the brand and model number or a picture will help, for my own sake, Thanks.

Regards,
John