Condo heat from hot water heater

JL325

I'm renting an apartment with a heating system that is no more than 10 years old. I can't for the life of me figure out how to get the heat on. The system pulls water from the hot water heater and cycles it through the AC unit. I've checked the breakers and the thermostat. The AC works fine. The landlord had a "heat guy" check it out, but was told the electrical components are working fine, that it's a plumbing problem. A plumber came, said the pipes are hot going in and cool going out, as they should be, and couldn't identify a problem.



Since I'm not familiar with this kind of set up, I have no idea what things I should look for to identify a problem. Anyone have any suggestions about things to check, or what kind of service person I could have check it out?