How to remove Delta Bathrub Handle

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.

There could be multiple reasons. In order of likeliness.
As a safety feature there are anti scald features of those faucets. Roman style tubs move a high amount of water and very possible there is a mixing valve upstream that is opening when the water is hot. Very quickly the hot water is evacuated and the mixing valve closes. Slowly heats up and the cycle repeats Or Incorrect cartridge in the tub faucet handles. Perhaps they installed the hot cartridge on the cold set and vice verse.

Or

Poor insulation on the piping but this would give te symptom of a long amount of cold then warm with eventual hot water.

I'd say rhe first solution is most likely. You can try and fill the tub at a slow rate with both handles open. The hot more than the cold.

Either way if you can find the mixing valve. Perhaps near the jacuzzi access panel or a nearby access box in the wall or under a sink you can possibly adjust the controls to allow higher temperatures. Keeping the mixing valve from opening as often. But this may not be so in an apartment building it could very well be in a mechanical room under he buildings maintenance control.

Also the other faucets don't exhibit this due to he flow control aerators keeping flow rates down in the 1gpm range depending on local code.