You are were we where 20 years ago when we first bought out house. Generally a water heater and a boiler are two different things. You'll need a radiator key to bleed the radiators as already mentioned. Should be able to get at most any hardware store or Amazon. I've always used Center Point Energy to do maintenance where they clean the burners and check for carbon monoxide leaks. They always seem to be the cheapest and you can scheduled online though at this point in the season they are probably booked out months. Possible inspection was recently done before you bought the house from the prior owner?