Where does the air come from

I have to purge the cast iron rad in the house every morning, my system is pressurized with auto purgers in the house and the boiler room should have no air in the pipes.

If you have a water leak in your system there is air in the fresh water being added. It does take a while to bleed out if you just filled your tanks

I have had the auto air purgers on occasion stick open or contract when the zone cools down allowing air in. After purging air if you can close the air purger valve, and check in the morning. this has happened to me with the purge valves that use a schrader valve.

Thanks for the tips . I hope it's a bad purger because there are no visible leaks as Huffdog suggested so if it's leaking it would have to be under the slab.

Turn off your mackup water and watch the system pressure for awhile to find out if you have a leak. I doubt it would be in a slab with continous runs of pex.

TS

I guess I'll have to install a pressure gauge. Thanks