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!

nicholas bonham-carter

starting point

get an accurate low-pressure gauge on the pigtail, tee'd off from the pressuretrol, so you can verify the settings of the pressuretrol. sometimes, when the settings are turned too far down, the linkage disconnects, and allows the pressure to run wild. unless your main vents are very undersized, there should not be lots of hissing. also don't use a setback, as it will not save any fuel unless for a few days.--nbc