I have a very old boiler that heats the home with the water in cast iron pipes in the floor - concrete slab. I recently added a second floor with a forced air furnace. I started up the new furnace and now the boiler won't fire. Pilot light is still on. I turned off the furnace and the gas line to it, thinking it was a gas pressure problem, but still no go. Where should I start trouble shooting this thing?

Thanks

Start by jumping the thermostat out for the boiler and then see if it comes on. If it does you have a thermostat problem.