Yet another, Atwood water heater problem

[I_Fish_2]

So, a week ago, the water heater started acting up. Sometimes it would work as it should, sometimes it would light and burn until the water was hot. When it did, it might not re-light when the water was running, and you'd end with a colder than wanted shower. Sometimes, it would burn a few minutes and shut off. Sometimes, it did nothing, as if it had a blown fuse.

I replaced the thermostat and eco, no fix. I took out the control board and had it tested, it failed. So, I replaced it with a Dinosaur board. Bingo, problem solved! It worked like a champ the last 3 days.

Until now. The wife used the shower, and the heater burned like it should. She's done, the heater heats and kicks itself off. A few hours later I go to take a shower, and I have hot water, but as my shower progresses, it gets cooler and cooler. When I get done, I check to see if the wife had turned off the switch, but no, it's still on. The red indicator light is not lit. I turn it off and back on, nothing happens, including the red indicator light. I checked the fuses, all good.

Oh, and the thermal cut-off switch, diode, or whatever? That's what the tech where I got the Dino board said probably caused the Atwood board to go bad. I was told to eliminate it. He said that was Atwood's instructions. I still have it, and may put it back in at some point, but it's not currently in the circuit, so it can be eliminated as a cause.

What am I missing?

[Old-Biscuit]

That 2A fuse on circuit board is for the circuit board.
Unplug edge connector and remove circuit board.

With a multi-meter set to ohms you can check board power track.
Meter negative lead to ground track of edge connector (green wire)
Meter positive lead to top power track of edge connector (brown wire)
No continuity......board is defective

If tests good then check valve track
Meter negative lead to ground track of edge connector (green wire)
Meter positive lead to valve track of edge connection (red wire)
If no continuity, this indicates a blown valve track.....board is defective

Check that neither t-stat/ECO spade connectors are making contact with metal pan as that will cause shorting.

[CavemanCharlie]

A fuse blowing, especially that fast, means a short to ground somewhere. Is there a wire somewhere that was rubbing on metal and got the insulation wore off?

[I_Fish_2]

Well, it's getting deeper. I came home this evening and decided to go ahead and check and clean the terminals and grounds. Everything was good and tight, although I did clean up the grounds some. Checked voltage and have 12.8 volts. With camper plugged in, I get 13.8. So, I flip the switch and she fires right up.

Great! Well, not really. For some reason the fuse on the circuit board blows. I replace it, have the wife flip the switch, and it immediately blows another one. What's wrong to cause that? I took the terminals off one at a time, so as to not cross them up, but, I double checked by the wiring diagram in the manual, and all are right.

Where to look next?

[enblethen]

Check the ground connection that is located behind the gas valve.

[I_Fish_2]

Thanks Old Biscuit. I'm thinking along your lines. I'm tempted to start replacing the spade connectors. I'm thinking one of them might not be getting good contact, and when I had them off and on the other day, it "fixed" itself temporarily. I already checked the grounds. They look ok, except there is no ground under the circuit board.

As to the thermal fuse, he said that the pop off valve seeps water that drips into the fuse, causing calcium build up and corrosion. That in turn causes a sporadic connection, and the constant fluctuation in voltage, in time, does the circuit board in. He said remove it per Atwood's instructions.

[Old-Biscuit]

The 'thermal cut-off' is a one shot fuse safety device that blows at 190*F and 'cuts-off' all DC power to circuit board IF a flame blow-back should occur. Flame shooting out of combustion chamber and up the side of RV is not a good thing.

Causing circuit boards to go bad :H It's just a thermal fuse.

AND obviously your OEM board wasn't the real issue as the new Dino board didn't solve problem (and thermal fuse isn't even in circuit)

You are having DC power issues. And they are prior to board because it isn't even trying or throwing fault light.

12V DC can check good but doesn't take much resistance to stop it.
Check terminal connections/spade connections on t-stat/ECO and especially the connector on board. Connections need to be clean and tight.
Same with grounds (on water heater frame, gas valve and electrode bracket screw and the one that is screwed down under circuit board)

On/OFF switch can have bad terminals/contacts also.

Which model of Atwood?
Need to use meter and follow path of 12V DC to see if it is even getting to board when it is not re-firing.