: i have a hot water heating system that sprung a leak and now that i stopped the leak seems to be full of air. Do I bleed the system with the furnace running or turn it off? I tried to bleed it with it running but the pipes clank like they are gonna blow! So I tried with the furnace off but then nothing seems to happen.
A HW heating system is always bled of air with the system shut off, (the boiler not running and the circulator turned off). If there is enough pressure in the system, (about 7lbs. per floor above the boiler) start from the lowest radiators and work your way up.
If you have a loop system with baseboard radiation, use the purge valves at the boiler for air removal.
Good Luck. e-plumber