Loud bang / thump noise at water heater

For about 3 months now I have gotten a loud thump / bang noise from my water heater. It's a single noise that usually happens once a day after taking showers, sometimes randomly other times. No more than 3 times a day. The water heater is about 1yr old. It's a heat pump style 80 gallon water heater. I turned off the heat pump to use electric elements only and problem still exists.

The first thing I tried was to drain out the water heater. After refill, the problem still existed.

Second, I turned down the water temp. I had it set at 138 and bumped it down to 128. Still no difference in removing the noise.

I continued to look into problem deeper and I discovered that my expansion tank had been failed and full of water. It was apparently undersized for the 80gal heater anyways. Figuring that was the problem. I bought a larger expansion tank and charged prior to install at the pressure of my water. I get 60psi as tested at water heater and around 50-55 at my outside spigots. I set the expansion tank charge at 50psi.

I'm still getting the thump noise. It seems to be triggered most commonly following showers or high hot water usage. It would seem tied to heating/expansion of hot water. I don't know if air in the line would cause a single random thump like this or not. There is no evidence of a problem while using the showers or faucets. They don't hiccup and function just as they always have. My pipes are all copper plumbing and the house is about 7yrs old.

Any thoughts or help would be appreciated.

If you had a company install it I would have it checked out. Most water heaters have a 6 -10 year warranty. Just by what you are saying it could be the control valve. It could be letting a little bit of gas out before the burner ignites and making a small explosion sound. It seems that the only time you hear the noise is when you run enough hot water to kick on the burner.

Thanks for taking the time to reply. This is a heat pump water heater. It does not use gas at all. It is all electric. I installed it myself, bought from Lowes. The water heater itself has a warranty, but the isolated nature of the problem noise would make it hard to prove faulty water heater to get replacement most likely.

Sorry I should have read your post again before answering. The only other thing that I could think of is maybe the bottom element is making that noise. Call the Mfg and tell them your problem. Their tech support may be able to help. Are you positive that the noise is coming from the water heater. Could it be a hot pipe expanding against wood someplace. Just trying to give you some ideas. Little hard when your not right there. Let us know what you find.

do you have a hot recirculating system connected to the heater.
could be a check valve slamming shut.

maybe some pictures of your system will reveal something you may have over looked.

Here is a video of the sound. https://1drv.ms/v/s!Amf2xsmeqUN0tEWWq7PHednNKkLW

This is a heat pump style water heater so notice the compressor engage around the 45sec mark and the bang noise come shortly after the 1:15 mark. I have reached out to GE geospring about the problem. They are currently reviewing it, however, they have discontinued the geospring line and passed support off to Bradford White. We shall see how that goes. Their initial response was it needed a Freon recharge. I think the noise is exterior to plumbing or internal water heater, but I don't know. Maybe the video sheds new light onto it.

I had a similar problem but I have a tankless heater
I installed a spring check on the cold water in
a do split the domestic hot water runs so I installed a hammer
arrestor on both hot water runs I think the check would
have do e it but I stalled the arrestors anyway

Have to figured out what was causing the bang? I am having this same issue with my 80 gallon GE Geosprings. Mine is now three years olds. A few months ago it started making a load bang noise late into a heating cycle. I thought maybe there were minerals and sediment in the bottom being heated and popping. I drained it. There were no mineral deposits but there was some sediment, maybe rust because the water in my other water heater (AO Smith) was clear when I drained/flushed it. I heard the bang noise twice while I was draining and flushing the GE water heater. That really surprised me. Maybe something about the tank itself is defective?

Yes, GE discontinued the geospring line and Bradford white has assumed support for the product. I called Bradford white and while they didn't seem to want to really work directly with a homeowner instead of a contractor, I was able to convince them to work with me through the issue. I put a water pressure gauge on the heater and video recorded the heater until the bang noise happened, No pressure changed during the bang noise. After sending the video to Bradford white and they reviewed it, they declared they thought the tank was rippled on the inside and the heating of water was causing the loud bang. My water heater was just at the 1yr age mark and they agreed to replace the full unit with a new Bradford white heat pump water heater. I had to find an approved contractor to do the swap and work with warehouse vendor that Bradford white uses for distribution. They agreed to reimburse me for the contractor expense, since I was within the one year warranty time frame. Since yours is 3yrs old that may be a cost you would incure if you can get them to agree to replace. I was really surprised they were willing to replace full unit so easily. This really makes me wonder if there is some known issues on these units. The new unit is a copy cat of the geospring design, just with Bradford white labels on it and since it has been in place for about 3mos now I've not had the problem. Good luck. If you have any questions let me know.

I thought expansion tanks need to be set at 50% of the water pressure

Wow, That was some bang.

pcride said:

I thought expansion tanks need to be set at 50% of the water pressure

Click to expand...

NO NO NO !!! expansion tanks have to be set AT the system pressure and can only be set without "system" pressure/ isolated.

pcride said:

I thought expansion tanks need to be set at 50% of the water pressure

Click to expand...

You want the bladder pressure the same as the system pressure.
Preferablly before you install the Exp tank or turn water system off and bleed all pressure off of system to set tank pressure.
If you have a tank that is pre-charged with 25 psi and you install on a system with 50.
The system will compress the air in tank until it equalizes to system pressure, making the tank much less effective.

Hello - I am researching this issue as Im currently having the same symptoms on my 3 year old tankless water heater. Is there a resolution? Thank you in advance!