Atwood Water Heater Problem

[NRALIFR]

I’m having a strange issue with my water heater. The data tag is in the image below.
The burner lights normally and has a good flame. I believe the water is getting as hot as it ever has.

After the burner has been on for several minutes, and the water is getting hot, I can hear the gas valve turn the flame off, then immediately back on. It will do this 5-6 times before it goes off and stays off. There may be a minute or two between each off/on cycle.

Everything is clean. The burner tube and ignitor probe were replaced about eight months ago when I had to remove the WH for another project. The flame isn’t being blown out, it sounds like the gas valve is being told to turn the flame off, then immediately turn it back on.

What do you think might be causing this. I have my own suspicions, but I’d like to hear yours.



:):)

[NRALIFR]

I’d be very cautious about running a WH for any length of time with the tstat and ECO switches bypassed to diagnose an intermittent problem. If this had been a solid failure, where the burner was going out and staying out when it should have been on, then yes, bypassing the switches briefly would tell you whether the switches were the cause or not.

That’s not how my WH was failing though. The burner was never turning off and staying off when it should have been on. The burner would go out, then immediately come back on. Until I started tapping on the igniter board, it only started failing at the tail-end of the cycle, when I was pretty sure the water was just about hot enough. Exactly when it would start failing wasn’t consistent, the time between off/on failures wasn’t consistent, and the number of times it would fail before finally turning off for good wasn’t consistent. The only thing that WAS consistent was the fact that when the burner turned off prematurely, it immediately came back on.

Considering how it was failing, I think it’s likely that had I bypassed the tstat/ECO switches after the first off/on failure, the burner would have turned on (which it should). Which would have told me what? Nothing, unless I let it run for ...............how long? How long would you be willing to let a WH run that is already very hot with the tstat and ECO bypassed? That’s where I think it’s getting risky. Tapping on the igniter board at least influenced the failure somewhat, but like I said even that wasn’t 100%.

The tstat/ECO switches were less than $10 including shipping. I’m also about 99.999% sure that even if I’d taken this problem to an expert RV tech for repair, I’d still be paying for the switches and the igniter board plus a couple hours of labor.

I only replied to point out that bypassing the tstat and ECO for an intermittent problem on a WH for anything other than a brief amount of time is first of all risky, and second may not conclusively identify the root cause.

:):)

[NRALIFR]

.

[dougrainer]

NRALIFR wrote:

dougrainer wrote:

NRALIFR wrote:
Thanks, that’s what I was thinking.

Cheap part too, I like it. :B

:):)

All you had to do when it started the malfunction was connect the ECO and Tstat wires together. If it still malfunctioned, your PC board was bad and you saved the cost of those cheap parts. Doug

That would make it run until the relief valve opened, right? That should probably be mentioned.

On mine, if I left the WH alone, the off/on behavior was happening very close to the end of the heating cycle. Just about the time I would be thinking that the water should be hot enough, it would start the off/on..............off/on.............off/on...............and then finally off for good. I only discovered after replacing the tstat/ECO switches that I could make it misbehave a little sooner in the heating cycle by “tonking” the igniter board with a screwdriver handle. But even then it wasn’t 100%. About half the time that I gave the board a good tonk, nothing would happen.

No big deal, the tstat/ECO switches probably would have been the next things to fail anyway. The foam cover over them was completely unstuck, so it needed some attention.

:):)

NO. This was being done for test purposes. You would connect the wires WHEN the malfunction started. Doug

[NRALIFR]

dougrainer wrote:

NRALIFR wrote:
Thanks, that’s what I was thinking.

Cheap part too, I like it. :B

:):)

All you had to do when it started the malfunction was connect the ECO and Tstat wires together. If it still malfunctioned, your PC board was bad and you saved the cost of those cheap parts. Doug

That would make it run until the relief valve opened, right? That should probably be mentioned.

On mine, if I left the WH alone, the off/on behavior was happening very close to the end of the heating cycle. Just about the time I would be thinking that the water should be hot enough, it would start the off/on..............off/on.............off/on...............and then finally off for good. I only discovered after replacing the tstat/ECO switches that I could make it misbehave a little sooner in the heating cycle by “tonking” the igniter board with a screwdriver handle. But even then it wasn’t 100%. About half the time that I gave the board a good tonk, nothing would happen.

No big deal, the tstat/ECO switches probably would have been the next things to fail anyway. The foam cover over them was completely unstuck, so it needed some attention.

:):)

[dougrainer]

NRALIFR wrote:
Thanks, that’s what I was thinking.

Cheap part too, I like it. :B

:):)

All you had to do when it started the malfunction was connect the ECO and Tstat wires together. If it still malfunctioned, your PC board was bad and you saved the cost of those cheap parts. Doug

[NRALIFR]

Well, the cheap fix didn’t fix. It required a more generous application of $$$’s.

The T-stat/ECO switches didn’t fix the problem. Turns out the igniter board was causing the problem. :M

Dometic Atwood Mobile Products 91367 P.C. Board

I found that when I ordered the #91367 board, it DOESN’T ship with the #92075 adapter plug that my WH needs, even though the pictures show one with the board. I had to wait for that to be delivered to install the new board. :M:M

I tested it today, and it turns off as it should now. :B

[NRALIFR]

Thanks, that’s what I was thinking.

Cheap part too, I like it. :B

:):)

[Old-Biscuit]

T-stat OPENS when water temp reaches 140*F=====Closes when water temp cools to 110*F
ECO trips at 180*F......will reclose at 150*F

One of them is malfunctioning....measuring water temp would pin point.

But T-stat/ECO come as a set so replace both AND clean up/tighten spade connectors on wires for t-stat & ECO (Brown/Red)
Also the ones for the 'thermal fuse' (it blows at 190*F and is a one shot device)

[enblethen]

Verify that the ECO and the thermostat is tight to the tank.
If they are, I believe that the ECO is opening shutting off the unit.
Thermosat/eco kit