steam radiators are hissing loudly and spraying hot water/steam

We need pictures. In particular of the boiler piping. Try to stand back so we can get an overall view. How does the boiler water behave, when boiler is firing?

Piping does not look bad. Water might need a good cleaning for starts

I suspect the pigtail is clogged and the pressuretrol is not seeing pressure beyond what air is trapped behind the clog.

sediment would sink, i'm pretty sure that is oil in the sight glass which will cause surging which will throw liquid water in to the system which can get pushed out the vents. if the water bounces around while it is steaming we can tell you how to skim it to get rid of what i really think is oil.

the hissing may be bad or missing or severely undersized main vents

since it is cycling when you play with the pressuretrol settings I don't think the pigtail is clogged.

radiator vents are notoriously unreliable. i got 4x of 3 major brands and within each batch 1 was not closing when steam would hit it.

"sauna" in your room = vent is not closing as it's suppose when hot steam hits it.

pressuretrols are mechanical devices that suppose to be calibrated but in reality ARE NOT. some, straight out of factory, are so whack that they don't work at all. the only way to make sure it works is test it on a bench (basic Y split with 1-5psi gauge on one end and a small hand pump to intro pressure into the test device), then set it by screwing in or out a screw on the pressuretrol's back. yes, not working pressuretrol will send too much pressure down the pipes and in turn to the vents BUT working vents will shut in that steam in the radiators soon after steam heats those.

introducing steam too quickly into stone cold radiators will cause the steam condense too quickly. you want to insulate as much of your pipes as possible.

On your comment 1. There is nothing in a radiator, It is a hollow chunk of cast iron — nothing more, nothing less.

If vents are hissing, there are really only two possibilities: they are defective or the pressure is too high. And, I might add, if the pressure is too high the vents will be defective very quickly.

Which goes to your comments 2 and 3. You are presuming that sincee the system works well the problem isn't with the pressuretrol or the pigtail. I beg to differ. Steam is, in some ways, oddly forgiving — and excess pressure is one of those ways. While it creates all manor of problems, what it does not usually do is keep the system from heating. Add to this that "the gauge does move" — if it is the normal 0 to 30 psig gauge, that almost certainly means the pressure is too high.

@mspsh31415
To clean the pigtail:

Shut off the electricity to the boiler

Remove the clear plastic cover from the pressuretrol, label the wires with tape and take a picture with you phone so you know what wire goes where.

Disconnect the wires and armored cable sleeve from the pressuretrol.

Use a wrench on the brass nut at the base of the pressuretrol to unscrew it from the pigtail.

Stick the handle of the wrench through the loop of the pigtail to unscrew it.

Flush the pigtail with lots of water and make sure it passes water.

Pour boiled water into the elbow fitting on the boiler where the pigtail screwed in and make sure that elbow is freely draining, if it isn’t, use a coat hanger to clean it out.

Put new teflon tape on the pigtail threads clockwise and reassemble following the reverse of these instructions.

Adding a 1/4” brass union and hex nipple above the pigtail will allow you to avoid having to disconnect the wires next time by simply being able to undo the union nut to unscrew the pigtail. Wash all new piping thoroughly with dish detergent and rinse thoroughly before installing to avoid adding new oil (or soap!) to the boiler water. It may be a good time to add a tee for a low pressure gauge as well so you can calibrate your pressuretrol settings to be accurate to the desired operating pressure range. I’ll post a photo here later tonight of an example pigtail assembly.

others can describe skimming better, but essentially you heat the boiler to almost steaming then turn it off, remove the cap on the skim port or open the valve, put a bucket under it, turn on the manual fill just very slightly until a stream of water about the size of a pencil starts running out of the skim port and let that go in to the bucket for maybe an hour or 2. you can turn the boiler on and off to keep the water near steam hot, that will make it more effective. if it was throwing all that stuff up into the mains you will have to do it a couple times over a couple weeks as the steam and condensate brings that oil that the surging threw in to the mains back to the boiler. You are trying to float the oil on the surface out the skim port.

Actually the OP's pressuretrol is the other type — not the one with the clear cover. But the principle is the same. Odds are it's the pigtail is clogged. they do that.

The only real caution is to mark — and possibly photograph — how the wires are connected!

The reason yours doesn't reset when you try too set it too low is just that — when you go to, never mind below, the bottom marking on the scale, that often happens.

8-way boiler cleaner

As did Hoffman, until they moved production to China.

Am I reading this wrong, I have a Pressuretrol subtractive I had it set at 2psi with a 1.5 cut out and I lowered it to 1.5PSI with a 1.5 cut out. So you set the pressuretrol to cut out at 0psi. You will never see steam at that setting. try 1psi with a .5 cut out. Your pressuretrol is likely malfunctioning based on your settings.