Suburban SW6 lights but drops out after 30+ seconds

[GenoB]

I'm a pretty good troubleshooter but this one has me going. My 10 year old water heater has been working fine but now will only light and run for approx 30 seconds + or - a few seconds.
a) Normal sequence to start up, 5 second wait, valve actuates, igniter lights gas, runs for 30 sec
b) I replaced the propane regulator incase the gas was dropping out or weak
c) Replace the igniter thinking it may not be sensing the flame is there (2 pin)
d) Checked the gas valve solenoids using 12vdc, they both work strong and click hard
e) While the flame is working, there is 12vdc present at the gas valve. When it drops out there is still 12 vdc present at the gas valve. Sounds like gas is shutting off inside valve but its not because of electrical shutting off ?
f) Took main circuit board to RV shop and it tested OK
g) Cleaned and checked all electrical connections on gas valve and main circuit board.
h) DC power is always 12.5vdc
i) Disconnected gas line from gas valve and at regulator and blew out with 30 psi air compressor, thinking oil might be blocking lines ?
j) There is no lp switch over, single tank with new regulator. I have tried another lp gas tank, same thing

I give up. I still think its a gas issue, either weak or blocked or the gas valve has some kind of mechanical shut off perhaps when gas is low pressure or it is just bad ? I don't think its going to be electrical since the gas valve still had 12vdc when iit shuts down. sometimes it will go right into the start up sequence after the flame goes out and relight immediately for a short time ?

Any ideas ?

[GenoB]

Yeah I did the same thing, got side tracked by the 12 vdc present constant. I had taken a wire and applied 12 vdc to each coil and listened to the hard click and came to the concussing it was working OK and passed on that ... I had thought about checking resistance early on and didn't do it .... Should have ... lol

Tanks for your help anyway, good advise...

[Old-Biscuit]

YEP......gas valve solenoids
Takes BOTH to hold gas valve open against the spring pressure

Should have had to test ohms earlier but when you stated you had 12VDC ON both I ignored the ohms testing
:S

Glad you found the issue.!!

[GenoB]

**** Issue Resolved ****

See earlier Posts ...

[GenoB]

Ummmmm... well food for thought isn't it ! I agree but my little Toy Hauler has always had about 12.5 vdc battery reading on my solar power regulator and when on shore power ? Same reading on my digital meter when checking wiring, etc.. Might be because of my old batteries perhaps ? Hasn't been an issue and when on solar panels I have power all evening (never use propane heater tho) and recharge during the day. Also have a generator if needed and always starts so .... I'm not sure ?

[BFL13]

Thanks for the follow-up! Really good work finding that.

OK, now my other question-- what's with this? "h) DC power is always 12.5vdc"

If you are on shore power, 13.6v converter, 12.5 is a big drop to the WH IMO. If on battery, 12.5 is about 75% SOC and is not constant--so not "always".

[Boon_Docker]

Really glad to hear that you got it working.

I had a similar problem with a gas valve years ago. The furnace would start and blow cold air until I give the gas valve a whack with a wrench. Then it would run great until until the next cycle.

[GenoB]

**** Problem Solved ****

I got to thinking about what could be starving the flame of gas and decided to look harder at the gas valve. I used my digital meter to check the resistance on each coil and found one was 45 ohms and the other had over a Meg ohms of resistance. Looking up the specs I found a good coil is between 30 and 50 ohms. Taking two wires from my battery I attached them to each coil separately and found one worked fine, the other would lock in but after about 30 seconds it would release and then go right back on. A thermal short !!! I suspect the coil would heat up and a wire inside would disconnect, opening the coil and letting the valve close. Then right away contact as it cooled off and open the valve again. Over and over again !

Bought 2 new coils at about $25 and guess what ! WORKS GREAT !

Intermittent problems as ALWAYS the hardest to figure out fine. Thanks for all your help on this, I learned a lot ! Geno B-

[DarkSkySeeker]

This is what was wrong with mine: https://www.rv.net/forum/index.cfm/fuseaction/thread/tid/29783932.cfm

[GenoB]

[GenoB]

[GenoB]

I have a feeling these last two posts may be the issue then.
a) I scrapped the tube where the gas burins, lightly with a brush and blew out with air nossle. Lots of **** came out. I did not do anything to the little orface at the begging of the round gas tube so if I clean the round burner tube where the flame is, will that help ?
b) It appears to vent out the front and that is clear. I will look into burner tube to see how that looks at the back.

[smthbros]

Verify the integrity of the vent system. Re-circulation of exhaust gas into combustion air may cause similar symptoms.

[Old-Biscuit]

GAS orifices are a metered hole/precision that allws the proper amount of gas to flow

Propane system is ONLY 0.4 psi....so proper/correct flow of gas is CRITCIAL

Orifice rusty up/rough looking and you have scraped it!!!!
REPLACE IT -----it is NO Longer a metered/precision device

And clean the burner tube also


Side Note:
Circuit board instantly drops DC to gas valve when flame is not proven/lost------INSTANTLY
Gas Valve snaps closed under spring pressure upon loss of DC to solenoids.

[GenoB]

To answer several posts
1) Other gas usage - No difference. I have turned on all 3 burners on stove and run the heater and no difference when I start the water heater
2) I like this thermoset idea, I don't see it anywhere except the one behind the black rubber reset button and I have checked that, it stays 12vdc on top and bottom of reset button
3) Well the orface is rusty looking and rough. I did scrape it a bit and blow it out with a air hose. Think this could still be the issue ? I should take it out and soak it win alcohol then air dry it and put back in ? This doesn't seem logical to disrupt the flame but I'll listen to the experts and try this today ?
4) Flame looks good, mostly blue with some yellow. It seems to slowly shut down when the flame it going out, sometimes I hear the igniter going off just before the flame goes out ?