How to descale residential boiler

draft34

Hi. I have a gas boiler. The boiler bangs and knocks very loudly after it warms up. The pipes running through the house do not. I thought all that noise was due to lime and scale build up in the boiler. I would like information on how to descale my boiler on my own.

nicholas bonham-carter

Is this a steam system? A completely tight system should not have taken in enough makeup water to produce huge amounts of scale. Acid cleaning any small buildup in an old boiler may expose some pinholes.
Some noise is from scale inside, the boiler, but louder more percussive sounds are caused by improper, or clogged supply, and return piping.
Post some pictures of the boiler, and its piping, and we can advise.—NBC

hot_rod

How old is it? As NBC noted boiler should not be using a lot of water that would cause scaling. Check for a leak if it is a hydronic boiler.

If it is hard water scale, an acid based cleaner will work well.

I like and use Rhomar brand, a few others are available.

https://www.rhomarwater.com

draft34

Maybe I'm wrong then. What else could be producing a banging noise? No its not steam its a water boiler.

hot_rod

Is the noise when the burner turns on and it starts heating up?

Banging could also be caused by a zone valve, or a valve with a loose seat.

Percolation is the sound that old water heaters make when they fill with sediment. The burner heats the crud in the bottom and it can make a banging, popping, moaning sort of noise. Same happens in a boiler that is scaled.

No harm in running a cleaner through the system, boiler and radiation.