Best Of

2:19 from start of boil to shutdown? No. Something is seriously wrong with the venting. Or, possibly, the piping to the main vent.

You say this is a vapour steam system. How, exactly, are the mains and dry returns vented? I've looked at the previous thread, but it isn't clear to me what was done about main and dry return venting.

The main vent on the dry returns, whether there are crossover traps from the mains to the dry returns or not, should NEVER close — never see steam at all. Once the boiler fires, you can feel the progress of steam along the mains — 20 feet per minute is not a bad sort of ball park figure — and that should be steady progress. If there are vents on the mains, they should close when steam hits them — likewise crossover traps.

I can't help but think that somewhere in there there is a significant restriction — but what it is I couldn't say without really looking at the system.

There is another possibility, however, which has occurred to me. Where are the vapourstat and pressure gauge connected? If they are connected directly to the steam chest — which is the usual connection, through a nipple or through the sight glass — is the vapourstat responding to real system pressure, or is it responding to pressure oscillations in the steam chest? If the pressure gauge is on the same pigtail, is it bouncing around as steam is rising, or is it rising steadily? Note that this is not related to surging water level! If the pressure gauge is bouncing around, it is likely responding to steam pressure variations as bubbles form and burst, not to the steady pressure found in the header — and the mains. This could be the cause of the quick shutdown, as vapourstats are quite sensitive to pressure spikes of this sort. There are ways to cure this problem. The best is to connect the vapourstat and low pressure gauge to the header, not to the boiler. Another is to use a snubber on the pigtail, but that is problematic as snubbers have a way of clogging.

Whatever, it ain't right.

Take a deep breath.

If the boiler sections were never cleaned in 60 years how could it not have soot? Of course it will after 60 years any boiler will have soot.

If it is clean now and the flame look good and blue you are probably fine

The tech you had is an idiot and should have come back and retested it with his analyzer.

He is just trying to sell you a new boiler

At over 60 years old you should think about replacement (budget for it) have it combustion tested by someone that knows what they are doing and if ok keep running it

Boiler do not ware out and shouldn't need replacement if not leaking