My shower in the master bath takes forever to heat up. We typically have to run it for 5 or 10 minutes before it is even WARM!!
Baths and other shower don't do this.
What could be the problem?

In my area the water heaters are located in the garage and the master bath is the farthest from the heater. All the water setting in the main and branch has cooled just setting in the pipe and must be run out before water from the water heater can get to your shower, However, this should only take a few minutes. Do all the fixtures in the master bath, like the lavatory, take that long to heat up or is it just the shower? Regards, Tom

Just the shower. You have described our plumbing set up except that the shower is free standing approximately 10 feet or so from the spa tub in which the water heats up just fine. The spa and the tub are equally distant from the water heater itself, however.
That is why it is so frustrating. Any ideas?

I think you have a partially blocked hot water inlet port on your shower mixing valve. Do you need help with cleaning it out or is this something you have done before. If you want help try to tell us the brand.

We are new homeowners. So no, have not done that before. The brand is Delta and the top of the shower handle says Monitor. Thanks.

OK lets start with removing the handle, then the rim that covers the valve, should justpull out and finally the escutcheon plate. When you egt this far come back. The water main can still be Ok at this point but we will be shutting it down shortly.

You know what? My husband is out of town and he is the do it yourself-er, not me.
I'll let him take it from here. When he gets back, we'll post again.
Thanks so much.