thumping pipes

[Richnj]

I have an on demand tankless hot water heater which works great. It is piped with 1 inch cpvc pipe. Temperature is set at 120, water pressure is between 30- 60lbs (well tank and pump) When a faucet is opened and the water heats up in the pipe, the pipes thump every few seconds. Not real loud but its noticeable. After several minutes the thumping will stop with the water still running. I have been thinking about installing a water heater expansion tank in the hot water line near the heater. Do you think this is the correct way to handle this? If not how would you handle it? Thankyou. - Rich in newjersey

 

[Terry]

It could be that the pipes are tight, and as they heat up, they move.

 

[Sponsor]

 

[Jadnashua]

You shouldn't have the hot water thermal expansion problem that is seen with a tank type water heater, and expansion tank probably won't help...it is the pipe that is expanding, not the water so much. The plastic pipe expands and contracts a fair amount with temperature changes. So, with that in mind, it is not at all unheard of for the pipe to expand while you introduce hot water into the pipe. Once it stabilizes at the new temperature (like a few minutes into a shower), those noises probably stop. After you stop running the hot water, it will gradually cool off, and the pipe will shrink back to its original size. Because this is likely slower, you may not notice it as much as when the shot of hot water started through the pipe after being off for a long time.

 

[Richnj]

Solved the problem!

What was happening was that the pipe wants to move as it gets hot. I put my hand on it and i could feel it creaking as it heated up. The plumber hung the pipe with plastic perferated strapping nailed to the joists. I noticed that it was nailed tightly and the pipe couldnt move easily. So i pulled the nails out about 1/8" on each side so the pipe was hung but loose and not touching the wood instead of being tightly strapped against it. Quiet!

 

[Cass]

Yup, thats what it was, the pipe was moving against the wood and making a snaping/ thud sound. Enjoy a quiet life now.