Knocking Radiators (Hot water heat)

timccarpenter

I've got a couple of radiators that are knocking as they heat up. Usually one louder knock vs several. I bled the radiators thinking there was air trapped at the top. No luck, they immediately spit out water and no air. Thoughts?

leonz

It is simple expansion like the ting, ting, ting you hear in baseboard radiators only greater because there is
more metal.

timccarpenter

So...no real way to avoid that other than longer more consistent cycles on the boiler to keep the heat more even and avoiding as much expansion?

ethicalpaul

Is it possible a supply pipe or the radiator is "sticking" against a piece of wood floor or framing and as the system expands/contracts it "snaps" across the wood making a bang?

You can try cut pieces of milk jugs to act as sliders to eliminate the "sticking"

Big Ed_4

Cast iron radiators , set the boiler temperature to 140* average 130*-160* depends on outdoor temperature , the lower the better .

hot_rod

Outdoor reset control on the boiler better helps modulate the supply temperature, keep the system running longer cycles.

Big Ed_4

I agree and like hot rod's thoughts . saves on fuel , increasing comfort and should eliminate expansion noise . Good investment for your system ...