Boiler cycle & hissing rads

EricinVT

First, thank you for the endless information found on this site!

My 100 year old home is heated with steam radiators by a 20+ year old oil fired boiler. There are two mains, each with a vent at the end of the line and 12 radiators on two floors. The boiler has a honeywell pressuretrol which is set with a cut-in at .5 and the differential at 1. My question is about the boiler cycle. When the boiler fires up, it doesn't cycle off until the end of the heating cycle. I thought it should cycle on and off as the pressure raised and dropped. Also, most of my radiators are very noisy. Within a couple minutes of the boiler coming on I can hear the air escaping, then they crescendo to a nice full house chorus of hissing. Some of the radiators eventually "click" but then start hissing again. The hissing continues until the boiler cycles off at the end of the heating cycle.

Where should I start? I'd like to tackle this in the proper sequence. Thanks!

BobC

Bad vent or blocked pigtail?

All that hissing usually points to main vents not working and presuretrols that aren't doing their job.



First I would make sure those main vents are working and also time how long it takes steam to the end of the main from a cool start. Be careful about using your fingers, steam will burn skin very fast.



Do you know if the pigtail under the pressuretrol is clear? If that pigtail, or the base of the pressuretrol itself, becomes blocked the pressuretrol won't sense the pressure and it will never turn the boiler off when pressure exceeds the setpoint. What does the pressure gauge read when the system is off and cool and then when making steam towards the end of a heating cycle?



Bob

Jamie Hall

Place I'd start....

(after checking the pressuretrol's pigtail, as BobC said) is with the venting.  It is almost impossible on one pipe steam to have too much venting on the mains -- so that's the place I'd go first.  Are there main vents on the ends of the steam mains?  If so, are they working?  If not -- you need them.  They will take care of the air in the mains as the boiler comes on, and the radiator vents will only have to worry about the radiator and the riser, and should be quieter.



It is not true that all steam systems will cycle on pressure.  It depends very much on the relationship of the size of the boiler to the installed radiation.  Most will, though, if the cycle is long enough -- say half an hour or more -- such as you miight have comiig out of a big setback (not recommended), or on a really cold day.