Hi,

We have a gas water heater which is about 10 years old. For the past month or so, the water heater starts knocking in the middle of the night, exactly at 2:15AM. It happens about 3-4 times a week.

The knocking does not seem to have anything to do with hot water usage. There have been days when we were out all evening, from 5pm to midnight. Then we come home, use some cold water for brushing teeth, washing hands etc. and then go to bed. Hardly any hot water gets used, and then that night the heater will start knocking at 2:15AM. And there are other nights when we run the dishwasher and laundry at night, utilizing hot water, and then that night the heater won't knock. Then there are other nights when we use the dishwasher at night, and the heater will knock. So it is pretty random, and doesn't seem to be related to hot water usage.

Also when the knocking is happening, one of the three pipes that comes out of the heater is shaking/making the knocking sound. The heater itself is not shaking. So I'm not sure if it's the pipe that is knocking or the heater (sorry to sound to clueless).

We are the second owners of the house. The water heater has never been flushed - by us or the previous owner. I can try flushing it, but from what I read on this forum, the flushing seems to help if the knocking happens due to hot water usage. But since our knocking seems to happen randomly, I am thinking that the problem is different, so I wanted your expert opinions
Please help!
Thanks in advance!

If you do not flush,(not drain) your heater on a regular basis it will build up mineral on the bottom of the tank. When the flame comes on it turns the water trapped under the mineral to steam and the steam escaping is what you hear. Let me show you how to flush your heater. Attach a hose to the boiler drain at the bottom of the tank. With the pressure on, open the boiler drain and let it run until the water runs clear. You will see a spurt of red,(rust) and some white grains,(lime or calcium carbonate). The whole thing shouldn't take more then a few minutes. Don't forget to flush it out every month. Your heater will thank you for it. You might want to consider cleaning the screens on your aerators if you have a high mineral buildup. If the problem still persists after you have flushed, you will have to drain the heater, remove the boiler drain and go up in the bottom of the tank with a wood or plastic rod, (not metal) and try to break up the mineral and flush it out. Good luck and thank you for rating my answer, Tom

It sounds like you have mineral build-up inside the water heater, let's flush the water heater.

Attach a garden hose to the boiler drain at the bottom of the tank. With the pressure on, open the boiler drain and let it run until the water runs clear.

Now flush out your hot water lines on ALL fixtures that are affected if any. Pull each aerator and clean the screens. Be sure you put them back together the same way you took them out.

If the above would not help it is time to change the water heater, Thanks.

John

Thanks Tom and John! We will try flushing the water heater and then report back. But any idea why it happens exactly at the same time (2:15AM) ? Are gas water heaters designed such that their flame will go on at the same time everyday?