Should I change my HW Thermocouple?

[Johnynorthla]

Hi all, my Dometic hot water heater model GC6AA-10E will not stay lit on LP, will work on electric.

If I stick my grill lighter in the burn a tube, I can light the hot water heater but then the gas valve shut off after a few seconds. Im very familiar with home hot water heaters and HVAC, I’ve changed many a thermocouple. To me this seems to be the problem but I’ve never worked on these units. Should I just start there? Change the thermocouple?


I had the rig washed yesterday, by a professional who’s washed it in the past for me. I had a discussion with him about not spraying water directly into any vents or grates before he started. And he understood fully. . I’m just hoping that this is a coincidence.


We rarely use the hot water heater on LP. I shut it off yesterday before it was washed. So forgetting to turn it back on all day, I switched it to LP knowing that’s the quickest way to get it hot water.

[Johnynorthla]

Looking further into my issue I’ve done the following;

tested the 2 amp fuse in the circuit board, it’s good.


Disassembled the burner tube, it’s very clean.


I removed and checked the water heater thermal cut off, and checked for continuity with an Ohm meter, it’s good.


The one thing I noticed is the electronic igniter does not spark, could this be the issue? When I light the burner with a lighter it light but shuts off after a few seconds. I can repeat this 3 times and then I have to do a reset by switching LP on/off again.

What senses that there’s a flame to keep the gas valve open, is it the second probe on the igniter?

Is it ok to jump out the thermal cut off, just to further test it?

Any help appreciated

[Old-Biscuit]

Spark Electrode has dual purpose:
*Provide high voltage for ignition (~2000VDC)
*Provide return path for flame sensing (milliamp current)


If Spark Electrode is NOT firing (CLICK< CLICK<CLICK)
*Bad Electrode/bad wire connection-bad wire, bad ground
(Check continuity of electrode)
*Bad circuit board
(DC goes from circuit board to gas valve AND spark Electrode at same time)

Spark Electrode Atwood 93868 $10-$15 depending on vendor
Circuit Board Atwood 93851 $107-$200 depending on vendor
(good vendor......https://pdxrvwholesale.com/products/...l-module-93851)
****Dinosaur Electronics has a replacement Ignitor Board. Better Quality
https://www.dinosaurelectronics.com/UIB-64.html




FYI:
Electric/Gas use same set of t-stats
*T-stat opens at 140*F/closes for reheat at 110*F
*ECO (Energy Cut Off/High temp T-stat) opens at 180*F and triggers FAULT Light
*Thermal Cut Off blows at 190*F when exposed to flame blow back
(When blown NO DC for any functions)

Wiring Diagram

[Johnynorthla]

Thanks old biscuit.

I’ve ordered a new igniter, very inexpensive, I’ll start there.


I’ve also ordered a thermal fuse cut off just to have on hand. The spade connection on it was a bit tarnished, I sanded it to a bright copper.


At least it still works on AC.


Thank you.