Odd hot water tank issue

[AndrewFH]

I am having some issue with my water heater that I have not been able to diagnose. It is a GE 50 gallon gas water heater. About a week ago, I heard a knocking sound while the dishwasher was running. After tracking the noise down, I discovered that the supply line into the water heater (which has the expansion tank on it) was knocking every time the hot water was turned on. I was not sure what was causing it, but thought perhaps there was air in the line. I opened the pressure relief valve for a couple of minutes and that seemed to stop the knocking. It happened again a couple of days later, but again stopped after I opened the PRV. Then two days ago, we found that we had no hot water. First noticed in the shower which is upstairs and far from the tank. No hot water would flow at all. It wasn’t that the water was not hot, but no water at all came out when you turned on the hot water tap. I went down to the kitchen, which is much closer to the hot water heater and tried the tap there. It ran for a couple of seconds, then stopped.
I went to the hot water heater and opened the PRV. Again that seemed to work as the water started flowing again. Yesterday I had the same thing happen, not hot water flowing. Again was able to get it flowing again by opening the PRV for a short time.
I am not sure what is going. There is not much in the hot water tank itself that I think would be causing this. Seems to me that it may either be the PRV is bad, or perhaps the expansion tank.
Could either of these parts cause the problems I am having? Are there ways to test the PRV and or expansion tank?
Thanks for any suggestions.

 

[SHR]

How old is the water heater? What model GE? What are the first 4 digits of the serial number?

 

[AndrewFH]

The tank was purchased in March of 2001 so it is 13 years old. It is a model SG50T12A. Beginning of the serial number is GENG 0201D1

Some additional info.
I'm not sure if the PRV is leaking. I checked the drain line and it is dry where is comes out. However, it seems to have a very small leak at the top where the lever valve is. I've worked that valve several times in case there was some debris stuck in it, and it seems to have stopped, but I won't know for sure until I check it later.
I also tried to check the expansion tank. I tried the valve on the bottom. The was a very small hiss of air (less than 1 second) and then nothing. No air is coming out, nor is there any water coming out. I used my tire gauge to check it and it does read 30 lbs when a faucet is open, but goes up to 54 when I close the faucet. So I guess it is working?

 

[phishfood]

At 13 years old, I would just replace it and all of the tanks, valves, etc, and be done with it.

That said, I am not familiar with GE gas water heaters. Do they have a short galvanized pipe nipple with a groove around the diameter in the hot and cold ports on top? If so, that is a heat trap nipple, which has a ball or rubber flapper check in it, which could malfunction and cause something similar to what you are experiencing.

Something has come loose, and is getting caught in a fitting. Discharging the T & P valve is relieving the pressure that is holding it in place, and letting it fall partially open.

 

[SHR]

The water heater is on it's last legs. The sound you are hearing is steam bubbles rising from the bottom of the tank and displacing the sediment on the bottom of the tank. Until the tank starts to leak you will be OK, just irritated. Put change-out water heater on your to-do list.

Thank you for the info on the age of the water heater. The serial number verifies the same info. You had a 12 year warranty on the heater...it figures. I am changing those heaters out on average after 10-12 years. A lot better than the Bradford Whites which have been keeping me busy at 6-7 year old average (with a 6 year warranty)

 

[plumbdrum]

Also when you change out the tank if you don't have one already good practice would be to install a CO detector in the area of the HWH, it is a new amendment in my state that any replacement of gas appliances or conversions going into a masonry chimney lined, unlined, exterior, or interior require a hard wired CO detector, we will allow battery for 30 days until the homeowner can get an electrician. This is in my state but I think it's a great code that all states should amend , just a suggestion.


Sent from my iPhone using Plumbing Forum

 

[journeyman]

The problem is the heat trap in the nipples. Remove and replace with brass nipples. Recommend replacing 13 yr old heater

 

[AndrewFH]

Turns out that water heater is bad. I planned on replacing the heat trap nipples, but when I checked the water heater again, it was starting to leak from the bottom and the area where the pilot light is (which had gone out again) had water in it.
I replaced the heater this past weekend with no issues. Everything seems to be fine now.