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If it is set up right the traps on the emitters should never close. The traps on the mains have to be working. The traps on the returns may or may not close depending on exactly how the return trap works.

It looks like very little has been done to this system since it was installed so things that don't work are likely parts that need to be serviced rather than things that are wrong.

The baseboard should have been piped two pipe . Right now pitch the element back to the valve . A free standing radiator would be my first choice …

Wow. Just wow. Not only is it a vapour system — and an early one — but everything is still more or less there! You must get LAOSH, and you will find your system, or at least the basics for it, in there.

I would suggest, in this order:

First, check all the traps. Any radiator which isn't heating the trap is suspect. If you find a radiator where the outlet from the trap is close to steam hot, that one is suspect too. Replace any traps which you even think are bad. Both Tunstall and Barnes & Jones make innards to fit them.

Second, you can try to get the valves to move — and WD-40 is as good as anything — but if the don't, don't fret it. If the traps are working they are in the nice to have but not critical category.

Third, buy a good low pressure pressure gauge — to 0 to 3 psig — and figure out where to put it. And put it. Best bet is going to be to put it on a T off of whatever pipe connects the vapourstat (which is set properly, by the way) to the boiler. Clean out that connection which you are at it. That will tell you what pressure you are really at, at which point you decide whether the vapourstat need to be replaed.

Now. Take a deep breath and find you system, or one as like it as you can, in LAOSH and study it. Go down to the basement and study the piping. Go back and study the diagram and texts some more. Until you begin to think you know how that thing worked.

You are going to be the expert on it, so take some time to really be the expert!

Don't do ANYTHING other than those three steps above until you are feeling pretty good about the system. Then work on bringing it back to its former glory.

One further thougth. That boiler. What condition is it in? If it's in good shape, leave it for the time being. Yes it is using more fuel that a new one might. But… for now leave it. However, when you do have to replace it, take care: the water line on that boiler is quite high off the floor, and you must match that water line with any new boiler — which may put it on something of a pedestal. Do it.

I suspect that this boiler is not installed in the USA so we have no way to tell the size of this boiler. I have no idea the size of a boiler that is rated in tons. A firing rate in BTU's, GPH, fuel type etc would be helpful. Now, my one recommendation is to never repair a flame safeguard controller regardless of your knowledge of that control. I have seen too many accidents being caused by a "self repaired" control. It was always a much safer option to replace the controller with a factory rebuilt or brand new device. I say this from past experience. You may be the best at repairing this control but the price may be much too high.

Now, as to what the problem is with the controls of your boiler and it's firing, a good service company is well worth the price. When I was still working, I had the replacement controls and the expertise to trouble shoot almost any firing system here in the states. So, before you make a wrong choice, call someone that has the expertise, PLEASE. Once it goes "BOOM" it is then too late too call someone. MY 2 cents.

For 1 1/4" pipe (OD 1.66") wouldn't the edr be .434sqft/linear ft?

I'll add one more comment. The MoM vents that I recently tried to clean out, even after soaking and boiling in vinegar then water…twice had tons of rusty chunks come out after they fully dried.

I'm thinking whatever the internals are made of are not corrosion resistant at all. The steam/moisture creates a ton of corrosion and rust on these newer MoM's. That is what is making them fail.