I have two bthrooms back to back, and all fixtures have ample hot water except one shower mixing valve. It is a temptrol valve. I have replaced the stem twice, replace the seats, cut the water lines in the basement to see if there was a blockage in the piping but cannot seem to find the problem. Every other faucet gets plenty of hot water.
I am lost at what to check or repair. Any Ideas ?

When you pull the stem did you try having someone else turn the water back on while you held a towel over the valve? This would help determine if the valve is the issue or the supply.

Your are not telling us what brand of shower faucet you have. Anyway, the temp-control valves are adjustable. You can increase or decrease mixture of hot & cold water coming through your valve. See if you can play with the adjustment first.

I thought Pete said Temptrol, that's a Symmons valve isn't it?

Hi all:

YUP! Temptrol is a symmons tub/shower valve BOB!. ;)

PETE...

You said you replaced the stem twice and still no hot water to the unit..

First thing I'm wondering is if this is new problem or old issue.. Then I wonder if you checked the temperature limiting screw under the handle of the unit (click on the attachment:Symmons Temptrol.pdf at the bottom left... the screw is referred to as T-34 in the picture... ;) ).

Here, remove the handle and you should see a screw that has a flat head in the slarge stem nut... loosen this screw a few turns and see if that restores hot water to the unit.

If that is not the issue.. then you need to establish if hot water getting to the valve at all just like Ballenger suggested. Here, shut water, remove stem, then have a friend turn on the water to unit (if can isolate hot and cold, just turn on the hot water) while you hold a rag over the valve.

IF/WHEN water starts to get hot have friend turn water off and then drop back and let us know... ok?

Anyway, check the limiting screw... let us know...

MARK