one loud bang as boiler cools

juanez

Hi again!

Got excellent help here just the other day... So I figured I'll ask again.

I replaced the water in my boiler this weekend, and yesterday dialled down the cut-in from 2psi to about .7-.8 (who knows, it's not exactly a precise control!) with a 1psi diff.

So with that done, I have just started hearing one loud bang from the boiler as it's been shutoff and cooling for a couple of minutes..

It sort of sounds like metal contracting, if that makes sense.
Only one bang.

The only google answer I found so far seem to imply there's debris in the heat exchanger and I would require a "powerflush".. now overall the water in the system seem pretty clean, only a little bit of discolored water comes out at the beginning when draining the system.... (could of course still be some issue with debris I suppose)


Any other clues?

ethicalpaul

I had a loud bang sound from my main when it would cool. There was a radiator runout that was piped improperly (with no swing) and it was putting the main under a lot of tension.

In the "heating up" phase it wouldn't make noise, but always one bang on cooling.

I repiped that radiator better so that the main was no longer under that high tension and it stopped occurring.

One thing to look for.

juanez

ethicalpaul said:

I had a loud bang sound from my main when it would cool. There was a radiator runout that was piped improperly (with no swing) and it was putting the main under a lot of tension.

In the "heating up" phase it wouldn't make noise, but always one bang on cooling.

I repiped that radiator better so that the main was no longer under that high tension and it stopped occurring.

One thing to look for.

"with no swing" - are you saying there was no "swing joint(s)" on the pipe?

juanez

tommay said:

When you say "replaced the water" do you mean you completely drained it, flushed and refilled? Sometimes clean water will come out if only draining it a little....it's when you get to the bottom when you get the nitty gritty stuff coming out.

Ah yes, emptied completely.

And after empty, while the drain pipe was open let the water main run through and out as well.

Jamie Hall

One loud bang is something contracting. Hard to say what. Even harder to get rid of. I'd not sorry unless it's bugging you.

This is steam, right? That comment about debris in the heat exchanger is pure nonsense for steam.

ethicalpaul

juanez said:

ethicalpaul said:

I had a loud bang sound from my main when it would cool. There was a radiator runout that was piped improperly (with no swing) and it was putting the main under a lot of tension.

In the "heating up" phase it wouldn't make noise, but always one bang on cooling.

I repiped that radiator better so that the main was no longer under that high tension and it stopped occurring.

One thing to look for.

"with no swing" - are you saying there was no "swing joint(s)" on the pipe?

Exactly. The main went into a tee and continued "around the corner" of the tee. The runout for the radiator continued straight then had an elbow straight up to the valve. Not cool!

juanez

Thanks for all the replies!

I babysat the boiler for some time, and I was off on the location - it sounds like the bang is coming from the main pipe.

Not much I can do about it, as the pipes are all inside the walls.