3 story house ( no basement)
Crown BSI138 Boiler
one pipe system ( total of 11 finned tube convectors) all slightly tilt to the steam pipe side.
2 main steam pipes (1 to the front feeds 4 convectors , 1 main to the rear feeds 4 convectors, return pipe feeds 3 convectors on 1st fl.)
only the main steam pipe to the rear has the air vent ( maid o mist #1, it used to be gorton #1) on it at the end of the pipe.
so the boiler was running every 10 mins and stop for 1 min because of Cyclegard LWCO, it was running like this for 2 hours without any pressure rises to let the pressuretrol shut down the boiler, and the 1-5 psi gauge didn't move at all, i have replaced a new pressuretrol with set 0.5 cut in and 1 additive differential. the convectors from the 2 main pipes slightly warm after 45 mins and get hot after an hour or 2, the 3 convectors from the return pipe were still nothing even after 2 hours of running.
some of the convectors i have installed angle air vents instead of straight ones, i don't know it will make any big differences or not.