Purging old boiler

Jimbo_5

Working on an old WM CGa 70,000 BTU and had to replace the 40-year old B&G 100 with a 007. But trying to purge the air from the system is awfully frustrating since the make-up water comes in soooo slow it's driving me crazy. Instead of a modern pressure reducing valve and an expansion tank, it has an old expansion tank with a strange valve attached to the return manifold.
What would be my best bet for purging the air from this system. Thanks

billtwocase

Pump purge it like you would antifreeze. You are circulating it's own water, and not added new water, or minimal amount. Plus side is you don't play bucket brigade. The back loves you for it. I do this all the time now when possible

Jimbo_5

Thanks, but I am circulating all new water now. I had to replace the old air vent from on top of the boiler too, so I had to drain the system. The feed water just trickles in so slow.

Alan Welch

if there is a nearby water heater,run a jumper hose from tank drain to boiler drain to build pressure quickly.

STEVEusaPA

Take a picture of that "...old expansion tank with a strange valve attached ...", and the near boiler piping.

Jimbo_5

Circulating now, plenty of heat. But I changed the T-stat from the 1975 one to a Honeywell T87k, and now it just keeps firing, shuts off for 5 mins and refires.

Jimbo_5

I have the tstat set to the lowest, the room is about 75° and it's still running.

SuperTech

That setup you have is called fill-trol. Next time you have to drain the system do yourself a favor and junk the fill-trol in favor of an extrol tank, air vent/air scoop or spirovent and a pressure reducing fill valve/back flow preventer combo.

Jimbo_5

Thanks, I think you are right.