Hi all,

In a major renovation, we replaced most of our old plumbing, and, added a new floor with new plumbing.

The water hammer took about 2 weeks to show up. It only occurs when faucets are shut off quickly.

Our plumber [after ripping open some walls to look for loose pipes (!?!)] installed a pressure reducing valve where the water enters the house. He claims it took the pressure from ~130 to ~60psi. No help.

Then he added a large hammer arrestor just inside that valve. Nope! Then he installed smaller hammer arrestors under each sink & behind the washer. Still no luck...

I read that ceramic-valve faucets can cause water hammer due to the abrupt shut off. Interestingly, our 2 "old" upstairs ceramic faucets now cause water hammer, but the same faucets didn't when we had only a single story house.

We have 2 Takagi tankless water heaters mounted outside the house. The plumber thinks they must be responsible for the hammer.

Any other suggestions?

Thanks,

Pableau