correct boiler pressure?

ward_hill

Note: i pasted this from my post on another web forum, but the pictures didn't transfer

i'm unsure of when this gas boiler was installed, but it was made by the same company as made the radiators throughout the house -- some are large old brass[?] ones, with scrollwork, etc., and the others are the more modern style plain cast-iron -- i think that the gas model was preceded by a coal-fired boiler with a two-pipe gravity system -- the two pipe system remains, but there is now a circulator pump







the boiler was recently shut down and drained in order to remove two radiators temporarily to accommodate some reno work -- after adding extensions and new valves, a plumber reconnected the radiators and began refilling the boiler -- i told him that i would monitor the refill and bleed the radiators, so as to avoid another hundo on the bill

no problems on the first floor, but a couple of the rads on the second floor wouldn't heat up -- so, i opened the pressure regulator and began adding water a little at a time -- eventually the last two upstairs got hot and were bled

when i checked the gauge, which measures boiler pressure in feet, it was somewhere north of 50 ft, with the thermostat set pretty high -- i was told by the plumber that the pressure relief valve was meant to open at 30 psi -- the gauge has a top reading of 70 ft [1 psi = 2.3 feet, so this seems about right] -- after i lowered the thermostat to return to a normal temp, the pressure seemed to settle around the 30 ft mark when the boiler was running, and would drop down to about 20 ft when it cycled off -- at this point, the weather was relatively mild -- when outside temps began to drop to freezing overnight, and the boiler was running more frequently, the pressure built up to around the 60 ft level -- this seemed kind of high to me, so i drained off water until it dropped to 40ish -- it's now back to running in the 30-40 ft range, dropping to 20ish when not running

there is a red needle that appears to have been set at 20 ft -- to the extent that i ever noticed it, i always figured it represented a maximum value, but i'm wondering whether it's actually the minimum value ... that is, pressure needs to remain at or above 20 ft in order to get enough hot water to the rads furthest away on the second floor, which is roughly 30 feet above the boiler room -- does this sound right? -- it's my understanding that the pressure raises the water, not the circulator pump -- in the dead of northeast winter, when the boiler is running a lot, would it be normal for the pressure to rise up to the 60 ft level before dropping down to 20-30ish?


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1870

martin

15-17 PSI

It sounds to me like you have an expansion tank problem to see that kind of fluctution.