Timer switch on thermostat heat call circuit?

As @EBEBRATT-Ed says, my first thought would be to replace the trap internals -- use a 6 point socket to fit, a cheater bar, a helper and a backup wrench -- or better, a good impact driver.

If that didn't work, I'd do two things together: first, invest in -- if you don't already have it -- a vapourstat and set it for 7 ounces cutout, 4 ounce differential. Absolutely no higher. Then having done that, I'd go around and use those Hoffman radiator valves for what they are intended (and it's not balancing): set each one so that the radiator gets hot on a long run across 80 to 90 percent of the width and no more. Then figure out how to keep people from fiddling with them.

(a side note -- if your main venting on the returns is inadequate, you may have cycling problems. And, worse, if among the failed trap elements are the crossover traps, you will either have to replace those internals or plug the connection on the dry return and put main vents on the mains. This fix is not optional).

Set up this way, the system will run just fine without traps. In fact, that is the way a system with the Hoffman valves was intended to run, and the traps were sort an additional safeguard, but not really needed, unless the boiler got carried away (coal boilers did...).

Or you could go the timer route. It's a kludge, but it does work.

I have had great success with 6 point socket and 18 volt 1/2" impact.

Grind the end of the socket to remove the bevel to get better contact on the cap if needed.

I do use a back up wrench to just be safe. After a few you get the feel of how willing the caps will be to be removed and may not need the back up.

You could just eliminate the trap guts and install orifices in the union of the supply valve union.
This is for about only 20% of the cost of new trap parts and you never have another issue of repairs.

I have done this on a few jobs.

You must determine the pressure typical of the system and calculate the orifices' size to heat only 80% of the rad capacity. I get the orifices predrilled to 1/8" and enlarge as needed based on charts that I have.

If you start small on sizes you can increase as needed.

It seems you are a "hands on" HO and would be able to master this.

@Zipper13, your thought process is the right direction to go. As you have seen already there won't be much support for it here, but I endorse it. No you really are not way off base. It is the least expensive thing to do by far.

Think about how the system would have run with the original coal boiler. The radiators could never have been full (or close) because the steam supply was continuous and full radiators would have roasted the occupants. So there is never an actual need to fill a radiator and therefore no fundamental need for a trap.

With the change to intermittent fire some sort of burn time limiting mechanism (definitely not pressure) is needed to control the firings such that radiators can never fill. I have done it for more than two decades now. You couldn't pay me to go back to the standard control. The heat this way is dramatically more even. Once over this logical hump size of boiler and devices at each radiator in a two pipe system become unimportant. I have 23 radiators and haven't fussed with a device on one of them for years and years.

Start simple and go from there. Happy to help if you like.

Good show @Zipper13. Stick to your guns. You are on the right trail with sound logic. You are also one of the lucky ones to have a 2 pipe system.

Consider a control strategy that skips pressure altogether. By the time you are getting anywhere close to measurable pressure you already have too much steam out there. Your timer should be a delay off from a temp switch on a radiator inlet after steam actually arrives to adjust a fill level, not a delay to next on from a pressure stop already reached. Much more even heat can be achieved this way.