Bathroom – Fixing Shower Temperature Not Getting Hot Enough

Sounds like there is something wrong with the plumbing in the shower wall or more than likely the shower valve or stem system. If you are renting this isn't your responsibility. Not sure of your state's laws but if there is an issue like this in most states you can give the owner 2 notices and a reasonable amount of time and they have to pay for your plumber.

Again if you are renting I would not fix this yourself no matter your confidence level. Because mitigating damages will be on you.

Put something in writing to the owner. Tell them it is the second form of contact. Give them a date a few days out and say if it isn't fixed by that date you will hire a plumber to fix it.

Background:

All new valves sold in the USA must meet a Federal anti-scald standard meant to prevent sudden surges of hot water. A typical inexpensive 'cycling' anti-scald cartridge works on pressure only, and does not sense temperature. For example you're showering and the sprinklers go off, the cold water pressure drops, and the valve will reduce the hot flow to match. The higher pressure source is throttled prior to the mixing valve.

In addition the valves have an adjustable limit on the mixing valve: usually adjustable with a plastic ring easily accessible after installation.

A great background video on this topic, showing a Delta brand single handle faucet, is at http://www.youtube.com/watch?v=mI2NZMadb1A . The video shows the 'cycling' pressure balance mechanism in action.

A cutaway of a typical valve is at http://www.popularmechanics.com/home/improvement/electrical-plumbing/whats-behind-your-shower-walls (Popular Mechanics).

These 'cycling' valves have lots of small parts: periodic cleaning may be required.

For your situation:

• Try and rule out a strong pressure difference between hot and cold as it arrives at this fixture.
• If you can install a two handle faucet, that obviously would solve the problem.
• If your base rough in unit is a 'Grohe Flex', you can insert different single handle models in place and try them (without re-plumbing).

A more expensive 'thermostatic' valve would not have the problem you describe: it would keep the hot line fully open until a certain temperature is reached, regardless of the cold line pressure. Grohe sells such models.