Sorry for the duplication, but I posted this in an existing topic but I didn't see the topic get bumped up for the experts to view. Nonetheless, here is my reply to a previous thread:

[www.plbg.com]

Ok, I am having this same problem, with the shower water not staying hot, and I am being sent in several directions. I've used this site before with TREMENDOUS results, so I'm back again with hopefully another easily solved problem.

This is a 2 bathroom house with an electric Rheem heater, a Peerless / Delta single arm faucet, where the shower distribution is about 99% master bathroom : 1% guest. I was having a severe problem where I was getting a poor mix of hot water in the master bath only. Every other faucet would give me scalding hot water within seconds, but the master bath was giving me lukewarm water. At first I thought it was the shower head, which proved to be defective, but it didn't solve the problem. All research pointed to the shower mixer valve. I changed that, and adjusted the scald guard to the hottest setting.

That didn't fix the problem, although it made it a bit better. Now I do get hot water but it does not last very long at all. Additionally, it seems like I have to turn the handle further to get the same amount of heat that I used to get. For comparative reasons, I took a shower in the guest bathroom - a nice HOT shower. No issues whatsoever. After that, when I was brushing my teeth immediately after, the water from the sink was still scalding. Typically, after the lukewarm / warm showers in the master bath, the water is lukewarm at the faucet as if I depleted all the hot water.

Have I missed something? Is there something that needed to be reset? I went through some old schematics and it makes mention of having a reset button. However, the rest of the house is just fine.

SUMMARY: hot water all through the house except the master bath. Changed shower mixer valve, no significant difference in performance.

Thanks in advance.



Edited 1 times.

The first thing that comes to mind and the most likely to cause your symptoms is a failing hot water recirculation system.

How would I check to verify? I have hot water everywhere else, including the sink in the bathroom with the shower.

Also, how would this be fixed? Is this something a basic DIY'er can handle or best to call in a plumber?

Thanks.

Any chance that you have a mixing valve at the toilet to temper the incoming water into the tank?

Sorry for the late reply.

No visible mixing valve at either of the toilets.

Another perhpas symptom:
Took a shower that was warm, no real heat but not lukewarm either. As I go to wash the dishes post-shower, the water is scalding hot at the kitchen sink and prolonged heat. Just on a whim, I turn on the shower and it seems hotter than it was before. Does that still sound like the recirc. system?

Additionally, where would I locate my recirc system?

Should it be at the furthest faucet? My water heater is located in my hall, right next to bathroom number 2, which abuts bathroom number 1. Then there is the kitchen faucet, and a small add-on in the garage. I don't recall seeing any valve or anything.

Help!

Some single handle faucets can be suspect for a cross-connection when the cartridge fails. It's like having the hot and cold connected, so, when you call for hot water downstream of it, the cold flows back through and mixes with the hot. You would not notice it when using the failed fixture though.
If you were to get the hot pipe to the kitchen sink hot, it should stay hot for a while.If you then ran the hot in the poorly performing shower, and the hot pipe to the kitchen sink got cold rapidly, you have your culprit. Do you follow?