purge cast-iron boiler after heat call ends?

R. Kalia

As I understand it, the hot water left in the boiler at the end of a heat call, plus the hot water left in the pipes (we have a converted gravity system) are a cause of reduced efficiency. But it would be relatively easy for me to wire up a time delay relay so that the circulator pump runs for a few minutes more at the end of each heat call, to purge the hot water.

now I also hear that cold return water is supposed to cause condensation, which somehow damages cast-iron boilers. So is it bad to purge the hot water with a circulator running of a time-delay relay? Or is it okay because the burners are now off so there are no more combustion products to condense?

DaveGateway

Post purging the boiler to the zones

would probably overheat the heating zones since their set temp was already reached. I always have seen systems like the the Energy Kinetics System2000 or Tekmar boiler controls post purge the heat to an indirect WH. Not to mention post purging is usually done only when the water temp is over 140°, not to cool the indirect.