Ever since our new propane hot water heater was installed it has banged as it heats up. I contacted the manufacture and they suggested I flush it and I did that to no avail. I have rotated the exhaust twister thing in the center flue to no avail either. Just wondering if anyone has a remedy that I am not aware of or haven’t tried?

Do you have an expansion tank above your water heater? Does it do this after the water is heated initially (fully cold tank) or after someone uses a small amount of hot water and heater comes on for a short time? Does the drain line from the temperature and pressure valve get hot after it makes the noise? Is the pipe taking the hot water out of the heater and to the faucets hard copper or do you have the flexible connection near heater?

As the water heats, it expands and has to go somewhere, the expansion may be pushing your pipe, causing the noise; an expansion tank will take up the expanding water and pressure. If no tank, the t&p valve may be relieving the pressure buildup; this would be evident if the drain line gets warm when the heater gets close to the set point. If either of these are the cause, you might have to leave one faucet barely flowing (open) to see if popping noise stops. If it does, call a plumber and discuss installing an expansion tank. if you have the set point too high, it will force the t&p valve to open, so turning them down 10-15 degrees may solve your problem.

We do not have an expansion tank and the copper piping is directly attached to the tank. The pressure relief valve does not operate so it isn’t going over pressure. The banging noise happens as the water is heating up. We also have a circulation pump running on a timer. At the scheduled times it does pull the now cooled water from the furthest faucet and stuffs it back into the HW Heater. Thought I would mention that but I don not feel that it plays in the noise since the pump can be inactive and the banging still happens.

I have a gas wall heater that does the same thing. As it heats and cools down it pops and bangs loudly. Its just expansion of the sheet metal in the heater. Its most likely normal for that water heater to bang and pop as the sheet metal in it expands and shrinks with the heat. My water heater crackles when its heating and occasionally loudly pops too. It’s 20 years old and has done that since day one. Its most likely normal and not much you can do about it.

The expansion tank would probably help the problem. The other thing to check is that the pipes have room to move when they expand and contract. They make a plastic insert that acts as a bearing to let the pipes move slowly. Without easy movement the pipe expands and builds up tension until it overcomes the friction with a bang. Tension relieved the cycle starts again until the pipe is fully heated. Check at a good plumbing store for the bushings.