Gas water heater help wanted

This week, I had to modify a gas pipe for a stove that I replaced so I turned off the gas at the meter outside for about ten minutes.

Since that time my gas water heater isn't working. The pilot is out and it won't restart despite a visible spark.

I'm guessing there is an air bubble in my gas line. Is it possible to "burp" or prime the gas line? When the knob is turned to pilot there is a cutout in the knob that allows the red button on the left side of the knob to be pushed - I tried that then tried the ignitor. Nothing... so here I am  

Water heater is a 2009 Ruud P2-40F1  that has only served my kitchen sink and dishwasher since 2015. It's certainly near end of life based on age - here's a photo.

Thanks

Oh nevermind. Found it on YouTube!

a little ironic that I am so used to getting good response here that I asked here before going to the tubes. 

I just had to hold the red button down for about 20 seconds before AND after lighting the pilot. Then switch it over to ON.

...video for future reference

Yeah.  Gas flows with such low pressure that it takes a long time to purge air out of the line.  Glad we could help!  

.... and the only time that happens to my BBQ is when there's a yard full of people.

Curtis73 (Forum Supporter) said:

Yeah.  Gas flows with such low pressure that it takes a long time to purge air out of the line.  Glad we could help!  

I knew I could count on GRM's help. 

There is a thermocouple in the pilot flame that closes a valve for the pilot if pilot goes out (eg the thermocouple gets cold).  That's so if the pilot goes out for any reason it will not pump unburned gas out.  The button disables that mechanism so that the valve stays open and you can light the pilot in the first place.  You have to hold the button long enough for the thermocouple to get hot or else when you release it the valve closes leading to no pilot light.

I am having this problem now. I already replace the thermocouple a few days ago because it wouldn't stay lit with the old one. Now it lights but goes out on it's own 1-4 hours later. When I restart it it won't stay lit when it's already warm. I left it off all day yesterday. It relit fine this morning and stayed on. 3 hours later the Pilot light was out again and won't stay fully lit after releasing the red button for a minute to change the knob from pilot to on. What am I missing? 

In reply to Sine_Qua_Non :

I'd recommend trying another thermocouple, it's possible you got a bad one.  Otherwise it would point to a problem in the pilot valve section of the gas valve and you would need to replace the gas valve itself.  

Sine_Qua_Non said:

I am having this problem now. I already replace the thermocouple a few days ago because it wouldn't stay lit with the old one. Now it lights but goes out on it's own 1-4 hours later. When I restart it it won't stay lit when it's already warm. I left it off all day yesterday. It relit fine this morning and stayed on. 3 hours later the Pilot light was out again and won't stay fully lit after releasing the red button for a minute to change the knob from pilot to on. What am I missing? 

I went through this nightmare with a gas fireplace last year. Even changed out the gas valve with no help. 

Turns out, there's an orifice below the pilot jet that can get gunked up and reduce flow. 

Then the pilot won't get the thermocouple hot enough to make the correct voltage to hold the valve for the pilot open.

Cleaned the orifice with a torch tip cleaner and it's all good now.

Took me a while to figure that out. 

You can probably find test specs for your burner assembly online by googling the make and model of the water heater. It should give you the voltage that the thermocouple should be putting out. Mine was barely in spec before the cleaning.