If you have a valve on the radiator, you can fairly easily bleed the radiator (rid it of air and fill it with water). To do this you will need a radiator key and a pan. Open the valve with the key (while heat is off and water is cool!) letting the air out. All the air will have been removed once water starts to come out of the valve. At that point, close the valve. Do this for all your radiators and you should have heat.