1.   In an effort to make the system more responsive, hydronic designers added a circulating pump to move the water through the system.

2.   In addition to the boiler, pipes, radiators and circulating pump, hot-water systems also have an expansion tank.

3.   On a hot-water system, the expansion tank should be drained, the circulating pump cleaned and lubricated and air bled out of the radiators.

4.   To drain the water from a hot water system, first shut off the switch to the circulating pump.