I could really use some help - I've had 2 visits from plumbers with no answer to my problem yet. In the master bathroom I have 2 sinks, a shower, and a whirlpool bath. For some reason about 2 months ago we started getting less and less hot water from the shower. The sinks still get hot water. The bathroom is at the furthest distance from the hot water tank so I realize it will take a minute or so to get hot. My hot water tank is fine and everything works in other bathrooms. It takes forever to get hot water into the shower and then it only gets luke warm. But here is a strange deal - while taking a shower (with luke warm water) I can reach over and turn on the hot water of the bath and all of a sudden my water in the shower gets hot.
The plumbers took apart the handles of both shower and bath and saw no problems. I have a 2 handle system for each (hot and cold handles). One plumber suggested that due to the cold weather maybe my pipes were frozen since they are in an exterior wall for the shower. He said the next step would be to do major work tearing into that exterior wall. Before I do that it sounds from other postings here that there could be something blocking the hot water valve? Is it possible to block the hot water valve to the shower but still go to the bath and sinks. Since buying the house 4 years ago we have had no issues other than water getting scalding hot when someone flushed the toilet. Now we can't even get it hot when we flush toilet. Obviously this has been very frustrating to go to the time and expense of 2 plumbers and still not have the problem resolved. Could it be something blocking a pipe? How can I fix this? What should I tell a plumber if I have to hire another one? I want to do everything I can to avoid tearing down and exterior wall but I can't handle much longer of this luke warm water. I would appreciate any help that you can give me.

First before I cqn help you very much I need to know the brand of your shower faucet. Also I would like to know if you have a circulating hot water system and also do you have a tank water heater or a hot water on demand type. Tell us this and someone might have an idea that will help.

I believe shower and bath are both delta. I assume circulating hot water system - 65 gallon tank - no on demand

I see pipes going to each sink but the pipes going to tub and shower must be under floor or in exterior wall - any thoughts?

i believe shower and bath are both delta. i assume circulating hot water system - 65 gallon tank - no on demand

You say that you assume that you have circulating hot water system, if this is true it could be the answer or the cause of your problem. It could be that you do not have a check valve on the circulating system and it is letting cold water back up into the hot water line. Or it could be that you have a check valve but it is stuck in the open position and the results are the same as if you didn't even have one.

I don't know how your system is piped so I am going to assume that it is plumbed the way that I would do it. I would put the return line in at the bottom of the heater where the drain fawcet is normally. In this line should be a Tee to attach a drain faucet and also in the line should be a turn off valve, and next there should be a fitting with no handle and has a nut on top, this is the check valve. It can be replaced or it can be taken apart and cleaned out, that is what the nut on top is for. There is also probably a small pump on this line. The water has to be turned off before taking the top off the check valve.
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This tells you how a check valve works.

Check Valve

Just before the loop enters the bottom of the hot water heater you might need to install a simple check valve. These are one way valves. This valve will prohibit in-rushing cold water from the bottom of the hot water heater from flowing backwards through the loop when you open a hot water faucet somewhere within the system.

Check valves are not always necessary. Some systems need them because of friction loss and other obstructions that make it easier for the hot water to flow backwards through the loop rather than the correct direction - from the top of the heater!

These valves can be installed after the loop is completed. Install it in the vertical loop pipe just before it enters the hot water heater. You might want to try installing the loop first without one and see what happens. If you begin to get cold water at a faucet when you should get hot, you know you need a check valve.

Great information - I don't have the skills for this - I will share with the next plumber - thanks for your help
If we do get the hot water to the shower as a general rule how long should it take to get hot? Shouldn't it be less than 2 minutes even if it is at the longest point away from hot water tank? Thank you