A.O.Smith Water Heater FCV--40-F00L010S19 Pilot Problem

[Jamie Jackson]

My pilot won't light.

Background:

• Pilot light has been going out for months now, and have had to re-light it weekly or so.
• Went on vacation for two weeks, and shut off gas to water heater during that time.
• Turned the gas line back on return from vacation (Saturday).
  

List o' current symptoms:

• Haven't been able to light the pilot since the return from vacation.
• No gas comes from the pilot tube when the pilot knob is turned to "pilot" and depressed.
• No gas comes directly from the pilot tube's hole in the thermostat/valve body (with pilot tube disconnected), when pilot knob's in same position as above.
• Gas flows to burner as expected, when the thermocouple is manually heated with a flame (not the pilot flame, obviously, since that doesn't work).

So, it seems that the thermostat/valve is messed up, but only the pilot portion. I haven't mucked with a water heater before this evening, so take my information/diagnosis with a grain of salt.

Got any suggestions? Humorous stories? Words of wisdom?

Thanks,

Jamie

[Cactus Bob]

WELL........ if what you say is all true , yes you need a gas valve . but thats the first one i have ever heard of going bad that way ..... recheck to see if gas is comeing out of the piolt port at the valve with the valve set to piolt and the button pushed down ...... no gas -bad valve

[Jamie Jackson]

Before I take the valve plunge ($), is there some more definite way to make sure there's no gas coming out of the pilot port?

• I don't smell or hear anything.
• If I block the port with my finger, and let go, there's no apparent build-up of pressure.
• If I rig up a drinking straw to the port, and seal the gaps with putty (play-doh... it's all I had), I don't get any bubbles when I put the end of the straw in water.

Seems like I've tried it all, but if anybody's got any suggestions...

Also, I just want to be sure: The thermocoupler has nothing to do with *lighting* the pilot (when the knob's pushed in), correct? I figure even with a totally busted thermocoupler, at least you should be able to get gas flow from the pilot port when the knob's pushed down in the pilot position.

[jambatt]

Remove pilot assembly and check orifice for blockage.

[Jamie Jackson]

[user=24427]jambatt[/user] wrote:

Remove pilot assembly and check orifice for blockage.

By the "pilot assembly," I assume you mean the tube that runs from the valve to the burner, and by "orifice," I assume you mean the end of the pilot tube near the burner.

The thing is, I have taken this tube completely out of the equation, since I've detached it from the valve body.

Even with the tube detached from the valve body, and with the pilot knob depressed in the "pilot" position, I'm not detecting any gas coming from the pilot port on the valve body. (This assumes that I'm trying to detect this gas in a reliable way, which I think I am, but I'm no expert.)

Has anybody seen the pilot line inside the valve body get clogged? I'm wondering if there's some other thing I can do (like hook the body up to my air compressor, or something) to try to salvage my valve.

(As you might have gathered, I am cheap!)

Also, can anyone confirm that the experiments that I wrote about in my second post (after Cactus Bob's post) are sane ways to try to detect whether gas is flowing from the pilot port of my valve body?

Thanks again.

[jambatt]

Have you turned the knob to off and let it sit for about five minutes so it can reset ?

[Jamie Jackson]

[user=24427]jambatt[/user] wrote:

Have you turned the knob to off and let it sit for about five minutes so it can reset ?

Yeah, it was off anytime I wasn't mucking with it.

[line]Update: Success!!  I took off the gas control valve, and hooked my air compressor up to the main line, and confirmed that no air came from the pilot port when the pilot knob was depressed.

I then forced of air into the pilot port  (backward air flow) with the knob pushed in, and eventually, something freed up, because air started coming out of the main gas input.

Then, I forced air into the gas input port again (forward air flow), and confirmed forward air flow when the pilot knob was depressed.

I reinstalled the gas control valve, and I'm back in business.

I let you know if the "repair" holds up, but it seems like this might be a good one to add to your collective bag of tricks.

Thanks for the replies,

Jamie

[line]Oh, one more thing, sort of a note to myself: It's pretty obvious when the pilot port on the gas control valve is working, I can block it with my finger, and notice the pressure build up. Also, I can smell gas easily.

Since it was messed up before, I didn't know what to expect in terms of flow, so I wasn't sure if my tests were valid or not. Turns out any of them would have worked. Now I know. ;-)

[RegUS_PatOff]

A few things to check:

Does no gas come out of the Pilot Port when the Button isn't depressed (Thermocouple cold) ?

Is there a "drip leg" (sediment trap) at the bottom of the vertical Gas Line drop ?

[Jamie Jackson]

[user=3641]RegUS_PatOff[/user] wrote:

A few things to check:

Does no gas come out of the Pilot Port when the Button isn't depressed (Thermocouple cold) ?

Is there a "drip leg" (sediment trap) at the bottom of the vertical Gas Line drop ?

Thanks for the reply, but I'm all squared away now, after going medieval on the gas control valve's ports with an air compressor.

Previous to the fix, I was getting no gas out of the pilot port in all positions of the knob. Now, I get gas to the port as appropriate.

The "repair" is still holding up.

Further, our thirsty dogwoods are, I'm sure, much happier after getting 40 gallons of drained tank water. ;-)

[wagstdy]

[user=3641]RegUS_PatOff[/user] wrote:

A few things to check:

Does no gas come out of the Pilot Port when the Button isn't depressed (Thermocouple cold) ?

Is there a "drip leg" (sediment trap) at the bottom of the vertical Gas Line drop ?

Jamie, I'm impressed you were able to accomplish what you did considering it was your first crack at a gas water heater. 

I think what Reg is getting at is......does the gas valve still shutoff the gas flow to the pilot with a cold thermocouple and the pilot button not depressed AFTER you've gone medieval on the valve with high pressure air?  If your pilot light gets blown out AND the control valve doesn't shutoff the gas after the thermocouple gets cold then you're going to have unburned gas escaping into your home.  It would be an easy test and worth the 5 mintues.

 

 

[Jamie Jackson]

[user=39200]wagstdy[/user] wrote:

[user=3641]RegUS_PatOff[/user] wrote:

A few things to check:

Does no gas come out of the Pilot Port when the Button isn't depressed (Thermocouple cold) ?

Is there a "drip leg" (sediment trap) at the bottom of the vertical Gas Line drop ?

Jamie, I'm impressed you were able to accomplish what you did considering it was your first crack at a gas water heater. 

I think what Reg is getting at is......does the gas valve still shutoff the gas flow to the pilot with a cold thermocouple and the pilot button not depressed AFTER you've gone medieval on the valve with high pressure air?  If your pilot light gets blown out AND the control valve doesn't shutoff the gas after the thermocouple gets cold then you're going to have unburned gas escaping into your home.  It would be an easy test and worth the 5 mintues.

Reg and wagstdy,

I had the same concern after "tampering" with the valve, but the pilot gas does shut off with a cold thermocouple (as it's supposed to).

Thanks for checking, though! I definitely wouldn't want to override the valve's safety mechanisms to work around the problem!

Jamie

P.S. Water heater's still going strong.

P.S.S. High pressure/temperature valve had a slow leak after having vented the tank while draining, but opening/closing it a few times seemed to seat it back, and it's watertight again.

[Jamie Jackson]

[user=3641]RegUS_PatOff[/user] wrote:

A few things to check:

Does no gas come out of the Pilot Port when the Button isn't depressed (Thermocouple cold) ?

Is there a "drip leg" (sediment trap) at the bottom of the vertical Gas Line drop ?

To answer the second question: I don't see anything that might be a trap, at least near the water heater itself. (Or would I be looking elsewhere?)

[RegUS_PatOff]

normally at the bottom of that vertical pipe, there would be "T" and an extra few inches down, to catch any sediment in the vertical pipe run, that would fall into the bottom of the "T" , but that wouldn't seem to happen in this set-up because of the way the upper "T" connection is, any vertical pipe sediment would settle in the upper pipes before it gets to the Gas Valve.