I live in a 5 story building with a sizable hot water heater. When I take a shower, the water will turn instantly ice cold if an upstairs neighbor turns their shower to hot. We have a single hot water pipe that comes up the chase to all apartments and then there is a "T" at each shower. When I get out of the shower (because it is freezing), I notice that the sink hot water is cold too. In addition, when the shower upstairs gets turned off, the hot water comes back within 1 minute.

Please help me figure out what is wrong so that I can have a nice shower. My landlord is open to suggestions and I think the 2 showers above me need low flow shower heads since this seems like a pressure issue and not a hot water volume issue.

Any advice?

Do you have a separate recirculating pipe or is the cold side used? Does the recirc pump work?

There is no recirculating pipe or pump. It is a one way system starting at the water heater in the basement and ending on the fifth floor.

Would installing a recirculating pipe and pump help the problem? Is the problem caused by a pressure differential that could be remedied with a looped system?

Possibly you could install a recirc system. May be better to increase the hot main trunk line.