Loud noise from tank when faucet is first turned ON, not off.

I have a condo we are renting and have been having a problem off and on with the water heater for a few years. The unit was new in 2004. It is a gas water heater and the condo has CPVC plumbing.

When you FIRST turn on the water at a faucet, you hear a very loud chugging, banging sound from the water heater. It doesn't make a noise when you close the faucet. We noticed this when we still lived there and now the tennant said it is making loud noises again. I have drained the tank before and refilled the lines and that seemed to help for a while. There was not an exorbitant amount of sediment that came out. And it doesn't do it while the tank is heating and the faucets are closed, just when you open the faucet.

Of course it sounds like water hammer, but again I have never heard of water hammer when you first OPEN the faucet. The only thought I had was maybe putting hammer arresters inline on the inlet and outlet of the water tank. But again, is it really hammer?

Thanks for any advice!
Ron

I'm not sure what it is, but it can't be water hammer, which is created from the abrupt stop off the water mass that's flowing. You don't have an equivalent flowing water energy to dissipate when opening up a faucet.

It could be a sort of water hammer caused by air in the line or tank. Air can move faster through a restriction than water and as a result surge strong enough to make a hammer like noise. The air however should be apparent at the faucet and that was not mentioned. Modern tanks also have anti-percolation valves in them that can make a clunking noise when the water flows and sometimes also when the water stops. The sound is right at the tank and can be quite loud.

It's most likely the rubber washer on the faucet.

I stayed at the Fairmont Hotel in Vancouver BC in Canada, and it was a freaking train wreck everytime I tried to use the hot water on the pedestal lav.
People from the next room were wondering what was happening in the bathroom.

Take apart the faucet and do the needed repairs.

You can also check to make sure that the shutoff at the wall is opened all the way. Those can get noisey too. A bad washer on a nearly closed wall shutoff can do the same thing.

Thanks, guys. I will investigate a little further. I am going to look at it tonight.

There is no air at the faucets when they are turned on. Also the noise happens no matter what faucet or valve gets opened, kitchen, bathrooms, dishwasher, washer. Very frustrating....

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OK I literally just thought of something. From what I am hearing if there were some sort of restriction on the inside of a pipe, that could be a possible cause right? I had added a humidifier a few years ago and I put a saddle valve on the flexible copper supply line to the tank. I removed the humidifier and I spun the saddle valve closed. Could the needle on the valve sticking into the pipe be a culprit?

Stand by the WH while someone turns valves on and off to see if you can see anything moving or to isolate it to a particular fitting or location. Also, double check your water pressure (a gauge only costs about $10 at a big box store). Do you have an expansion tank? If you do, is it waterlogged and has failed?

Dont know why know one has posted this, but is it the hot and cold water that do that? One time the dip tube on the tank was dangleing around on me when you turned a faucet on, one time it was a trap primer hooked to the tank which was in a drain pan. another time it was the shut off valve on the tank was rattling

If it is a "popping" sound, then it is "superheated water" in rust nodules inside the heater which changes to steam when the pressure drop because a faucet is opened. It wil usually go away after a few months as the nodules "break down" so they cannot trap water inside them.