Steam heating system-losing steam
I have a steam heating system. Last winter, it would lose steam consistently during heating season. I'd have to refill it once a day. I changed all of the air vents last year to the 'tall' cylinders--larger upstairs, smaller ones down stairs using the advice from the local hardware store. No effect on steam loss. I could hear them hiss and then click shut reliably.
Recently I had the unit looked at for a different reason and mentioned the loss of steam in the cold months. The repairman did not see any rust on the boiler, nothing obvious around the base of the unit.
I bought some new air vents this weekend-'Maid o Mist'--more of a drum style than the tall cylinders. Not much change. One radiator with the new Maid O Mist just kept putting out steam with no shut off (this one is closest to the furnace). The air vent appeared like all the others that hissed/shut off (although it took longer for these to shut off than the tall cylinder type).
There were two units last year that were leading at the turn off valve--fixed that with graphic rope.
Before I call the repair man back, what else can I look for and fix as a home repair person? There is no indication of wet ceilings/floors that I can see.
Any other ideas or is this a job for a professional?