In the bathroom of this rental is a tub with a shower diverter. It's an older setup with a hot & cold faucet and a center valve (one direction diverts to shower, the other to the tub faucet).
If I turn on only the hot water, I get hot water for 30-45 seconds, then it goes cold. The water is heated by a stove oil fired boiler which also heats the building via radiators.
If I go to the bathroom sink, or to the kitchen sink and turn on only the hot water, I have hot, hot water for virtually as long as I keep the faucet on.
One additional issue is the water temperature is set way too high. At the kitchen faucet, I measured the temp, and after about 30 seconds, the water temp stabilizes at about 185 degrees.
Too high, seriously dangerous too high, but the landlord insists the boiler has to be set that high, or "there won't be any heat in the winter, and everyone will complain about THAT."
This same landlord also argues with me that insulating the supply pipes to the radiators 'wastes' the heat in the pipes, and has forbade me insulating them in our apartment, even though they are a serious safety issue.
I don't see how the high temp setting would cause only the bath tub to have limited hot water, but after seeing what the hot water did to the drain pipes in the third floor bathtub, right above our second story bathroom, I'm wondering if the 185' water has damaged the diverter. [We have a suspended ceiling in our bathroom. A leaky hot water faucet in the 3rd floor bath tub leaked 185' water into the PVC drain pipes, causing them to deform, then leak, then soak our fiberglass paneled ceiling, (like in a typical office), which then caved in at 6:00am one morning.]
He ended up paying me to fix the plumbing and ceiling, and in 40+ years of construction, I've never seen anything like it. I had to replace everything from the strainer on the tub to the junction with the 3" cast iron vertical drain. It was all distorted and melted from hot ass water.
Anyway, we have the 185' water, and still have to take cold showers most of the time because of this strange issue with the diverter in the tub.
I have tried every combination of adjustments, but can't figure out what's wrong. When I take a shower, I've noticed I get MORE hot water, if I open the cold water faucet further, but at some point, it doesn't help.
Any ideas? Wild guesses? Could the 'clowns' have installed the diverter incorrectly? It's been replaced in the last 5-10 years, from what I can tell.