Mark,
Welcome to "time-to-get-to-know-your-car" time. I'd suggest that you examine the car for some simple/cheap fixes: 1) are the hoses (next to the heater valve) hooked up to the heater box - or bypassing it? 2) Is your water level in the radiator full? 3) Did the PO remove the thermostat?
You might check these 3 things while awaiting input from others...
If you have an expansion tank on the firewall more than half full, any 'extra' water should boil off and drain while the engine is cooling (and shut off) until it reaches its steady-state level. This won't be worth checking until you can get/keep heat in the engine.
Best wishes,