Why is the hot water in my tub fluctuating between hot, warm and cold?

Question

I've been living for a year in a 1985 (or so) 8-floor condo in the NYC metropolitan area. The building is well managed. I have a kitchen and a bathroom with both a separate shower and a jacuzzi/whirlpool tub installed. The tub is a Kohler ('Devonshire' model). The 2-handle faucets looks like from Pegasus ('65602 Estates Roman Tub Faucet'). Hot and cold water works fine everywhere in my apartment but the tub.

** PROBLEM **

When I turn on the hot water faucet of the tub (assume it's the only thing running water), I get first very hot water as expected for a short moment, then it becomes warm and cold. I have to play around with the faucet (turn off, or turn more or less) to get some hot water again. But the cycle will repeat. It's frustrating.

I'm not sure what is causing this. The problem has been there since I moved in.

Elsewhere, the water works fine (kitchen, bathroom sink, shower) with this minor note: In the shower, I have a Pegasus single handle with a typical problem. Assume turning the handle from Right to Left, starting at the 6pm position. - From 6pm till 1pm, I have increasing hot water as expected, - Then at 12pm, it shuts down all water. - Then continuing from 12pm back to 6pm, cold water (not sure if there's any hot water at some point, I've never tried long enough but I doubt). It's not a big problem for me since I've been able to take showers, so never had the need to fix it. I'm mentionning the shower just as FYI, in case it could have anything to do with my hot water problem in the bathtub.

Oh yes, jacuzzi button works fine too.

I have the feeling all I need to do is replace something in the tub's hot water faucet, but not sure what. I've had hard time finding a PDF specs or manual/instructions for that Pegasus 65602 Estates Roman Tub Faucet.

Thank you for any help or advices.

Answer 1

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.