First off. This site is awesome. This is my first post but i have been a reader here ever since I bought my first steam heat system (it came with a free house) 2 years ago. You all have been invaluable in getting me as far as i am now with my ill maintained system. I've replaced the presurtrol with a vaporstat and 3psi gauge (pressuretrol as safety), I've added main vents with 2x Hoffman 45's, ripped out and re-piped a leg that was done in pex by some bone head contractor, and replaced all of my Rad vents with hoffman 1a's. And i recently added an ecobee thermostat (mostly because my previous honeywell got destroyed by my current contractor)
With that said its time for me to ask for a bit more specific help. I have a relatively big 1 pipe system (4000sq ft 3 story house) with about 10 rad's of varying size. The boiler is a "newer" dunkirt model 299k btu. All of my fixes so far have made a TREMENDOUS improvement, but I need to do a bit of fine tuning now. So here's my issue.
When the system is working hard (recovering from a few degree setback, or when its quite cold out) i get some hissing from the rad vents. It only starts after the Rads are completely full and warm and happens to all the rads, not just one. My thought was that my system was over pressured, but this happens when the gauge still reads 0.5psi. After the hissing starts the boiler starts to slowly build pressure and will go up to 1.5 psi then start to cycle off on pressure a few time before the call for heat stops.
The only thing i can think the issue would be is that my main vents are undersized??? I took them off today to make sure they were working (blew air through the bottom and it came out the top?). Any help (or suggest for other improvements based on my photos would be well appreciated and repaid with a virtual beer or high-five.