How do I replace a backflow preventer valve on the cold water supply side to my furnace?

Hi Pzale...

If the backflow preventer valve (BFPV) isn't isolated by a shutoff valve on both sides of the valve then you will need to shut off the main water supply into the boiler and you will need to drain the water out from the boiler and radiators (or baseboard) to just below the BFPV... then you can replace the BFPV.

To drain the water from the radiators or baseboard you will need to find the VENTS to each unit and open them to let air in so water can drain.

Once the BFPV is replaced you will need to fill the boiler and the radiators (or baseboard) and purge all air from the system through the vents... OR there may be a fast purge valve with a shutoff valve just above the circulator for each zone.

Let us know more about your system. Are there isolating shutoffs? How old is the system? A picture of the system would help us to lead you down the best path... ;)



MARK