Webster Air Vent blowing steam

did you skim the oils from the new pipe off of the boiler?

The guys above. That vent blowing steam is a symptom, not the problem. As was said, steam should never, ever reach that vent or be in those pipes. So… two possible problems. The easy one is that the system cutout pressure is too high. The boiler should cut out at no more than 8 OUNCES per square inch (half a pound). Less would be better — Websters (and most similar systems) run just fine on a maximum pressure of about 6 ounces.

So step one. Get down to the boiler and reset the pressure cutout device to a cutout of 6 ounces and a differential of 3 ounces. If it won't go that low, get a vapourstat and use it instead.

Then the second possibility is a failed trap somewhere on the system. Could be almost anywhere, so you may have some detective work to do. May be more than one trap…

Actually there is a third: in the work moving that pipe you reference, some piping intended to be a water seal may have gotten changed. Look for that, too.

Edit: and one more thing. Don't change that vent until you find the real problem…

Honest timber!

Any one of the traps could be the problem. Or several of them… or there may be crossover traps between the mains and the dry returns (probably are) which have failed.

Get the pressure under control, and then run the system long enough to get the radiators could and hot. Look for traps which are passing steam — the outlet pipes will be steam hot. Then replace the elements in any traps which have failed (Tunstall has the replacements — tell them what you need). Sometimes the problem is bad enough that the you can follow a warm dry return back to a failed trap! Makes life easier…

But as I said above, don't even think of worrying about that vent until you have fixed the problem(s).

Stop trying to troubleshoot the traps.

Traps wear out.

Count up the traps and the model #s and order replacement parts and change them out.

Its a mechanical part that wears out.

If you had a 1935 water pump in your car that started leaking would you 'troubleshoot it" or change it?

replacing them all is probably most economical.

if you want to try to track down the failed ones, start looking as the system starts to heat. after everything is hot you wont be able to tell where the steam in the returns started. the steam may also flow through the mains to radiators with good traps that have not closed yet too so you need to start with where you first start seeing steam in the returns. if the valves still work you can close those radiators that you think have bad traps and see if you still see steam from that place or in the returns at all

the first place steam gets in to the returns might be through the crossover traps at the ends of the mains. look for them, there likely are traps at the ends of the mains to vent the air out of the mains and in to the returns.

don't worry too much about the pressure, lower is always better but since it has traps it shouldn't start having problems until something like 2 psig rang if the traps are good and any water seals are deep enough

water hammer or higher pressure can destroy good old or new traps which is another reason to replace them all if they are old, you find and replace a bad trap then another trap causes hammer and destroys that brand new trap.

Once you fix the traps, you won't have steam blowing out of that vent.

This is true. And you won't need to replace the existing one — but it won't hurt, except in the wallet.

I might note, though, that if you DO replace the vent WITHOUT replacing the traps, the system will likely work considerably worse than it does now, if it works at all…

BINGO! Remove that improperly-installed crossover pipe, cap the runouts and I'll bet the problem disappears.

Why are they removing those radiators? That will result in those rooms being COLD!

if that is there, there may be other surprises waiting for you.

Yes. Fix this and try it again, see what happens.