How do I get to the pipes? All water poured out of water line in ceiling going to upstairs radiator

Out of the blue - ALL the water from my heating system POURED THROUGH my ceiling on the first floor. (house is about 90 years old - gas baseboard radiators) It poured out of the ceiling fan fixture - likely an easy path out - so I'm not exactly sure where the pipes run. Above the place where the water poured out - is one of the baseboard radiators upstairs at the front of the house. So I assume one of the pipes going to or from that spot - has cracked. The question - how do I get to it to fix the pipe? Upstairs - it's hardwood floors. Downstairs - I have high ceilings and plaster/lathe ceiling with old-school (horrible) insulation above the ceiling. Fluffy stuff - no idea what it's made of) I know how plumbing pipes run to/from bathrooms. You have to go to through the floors of the bathrooms -not up through the ceilings to get to the pipes. Is it the same with the pipes for the heating system? Do I have to take the hardwood floor up near the radiator - and follow the pipes out until I find the problem? It'll be the flooring AND the subflooring, I assume? HELP! (it's getting cold!) Amy