Steam radiators that sometimes work
I have a 75-year-old house with steam radiators and a gas furnace. Some of the radiators work fine, most of the time, then suddenly they don't, while others that usually don't work will suddenly start spewing lots of heat. It doesn't appear to have anything to do with the steam vents (those bullet-shaped appendages on the sides of the radiators)--I've experimented by removing them completely, with no results. The valves are all fully open, as far as I can tell.
You may have a faulty pressure control,..."I doubt it" though, but from what you are saying, it may not be developing enough pressure to deliver the head of steam to your radiators,..and the again it may be spurattic. Most residential steam settings are set at .5 to 1.5 cut-out. I wish there was an easy answer for this. There are about 7 different pipping arrangements that you can have,but Call your local contractor and make sure they work with steam boilers.