Hot and cold fluctuation

[Elctbreaks]

I recently moved into a pre-war NYC apartment. The shower has 3 knobs, one for hot, cold, and tub/shower head control. The issue I have is that the water fluctuates between cold and hot (scalding, actually) every minute or so. The pressure remains constant and great. Sometimes, when the water is cycling back to hot, it will be steaming hot with the cold water knob open fully and the hot water knob open just the slightest amount. I cant seem to replicate on the kitchen sink or bathroom sink. What ends up happening is, the water will run at a decent temperature for a bit and Ill have to use that time to get wet, shower and soap in between while waiting for warm/hot water again, then quickly rinse off. Its not the end of the world, but a consistent shower would be nice to have again in the future. Any thoughts?

 

[frodo]

i would say the diverter is bad, and needs to be replaced, call your land lord and tell him to get on it

 

[Mr_David]

I dealt with this on numerous occasions with multi-unit buildings with similar issues
Many things can contribute to this.
Common water heater for the entire building had a different cold water supply to the heater. It had it's own pressure reducing valve and was not balanced with the common cold service to the building.
Or the cold service main to the building came into the building on the far opposite end of the building. It would branch off to various units before it reached the water heater. That caused an imbalance. But that is unlikely that happened.

We had a building that had these problems but sometimes only 1 or 2 units would have a problem.

Some times the fluctuation is caused by worn and loose washers in the valve.

Solution: Rebuild the 3 handle valve ( Price Pfister ) with new stems and seats.
Remove the super water saver shower head and any flow restrictors in the new one. ( the fluctuation wasn't noticeable with a better volume shower head )

 

[journeyman]

Code states multi dwelling needs to have pressure balanced valve you are getting the spike because it is not pressure balanced

 

[Elctbreaks]

I hope changing the diverter or replacing the 3 piece set will work. The apartment is above a recently added restaurant downstairs and the water heater was added recently, as well. Hoping some serious plumbing snafu hasn't occurred.

 

[journeyman]

Install a pressure balanced shower valve