Intermittent Hot Water Pressure?

Sometimes I have hot water and sometimes I don't. I live in an apartment, but I have my own water heater (no sharing) and it doesn't seem to be related to how much hot water I have used in a day or what time of day it is. When the hot water is not working I only get a trickle from the faucets (this is throughout the apartment) when I only turn the hot tap on. The cold water still works fine. There doesn't seem to be a leak anywhere, and when the hot water works it works very well. It is an electric water heater and the city water supply (not a well).

I know this is my landlord's responsibility to fix, and he has come out to look at the hot water heater, but he is an older gentleman (unfamiliar with the internet) and hasn't been able to determine what the problem is. If anyone has any ideas I would be grateful!