[jr235]

When we flush the toilet, there is a knocking noise in the plumbing system. sounds like it is in the pipes all way up the the hot water tank in the attic. We just had a recirculation pump put in for improved hot water issues. What could be causing these knocking sounds that last about 2 minutes after flushing a toilet? Thanks for any help, Ron

[DetroitRob]

It sounds like unsupported piping banging around.

[IFIXH20]

Does it happens with all your toilets or just one particular toilet ?

[jr235]

Mainly from the guest bedroom toilet, we have 3 1/2 bathrooms

[IFIXH20]

The guest bath toilet fill valve and/or stop (shutoff valve) may need replacing if the noise is not that present at the other fixtures.

[stevemachine]

Sometimes shut off valves that are half open can cause water hammer, I would check that first. I've experienced that before for sure

[Haworthplumbing]

Has it always done this? The drain pipe could be passing through a very tight hole and be contracting then expanding again due to temperature change.

[pursable]

I agree with ifixh2o the toilet fill valve could be bad and needs replacing or repair or possible shut off valve rubber washer inside has come loose inside valve and is vibrating when water is running thru it. I have run into this alot because shut off valves have gotten alot cheaper and the manufactures have just press fit the rubber washer onto a stem inside the valve. Not a great design.