Hot Water Just stopped working

[mmcbride56]

Ok, so I am not what you would consider a newbie as I have been RVing in one form or another for about 40 years. I often do my own troubleshooting and repair for all things mechanical. I have even changed out a bad hot water heater element and thermostats.

The thing is, I am not 100% positive I have a thermostat issue but I am thinking that is the only thing left to try. I hate to have to remove the existing one as there is this form pad "glued" over the access to it.

For some background:

• The MH is a 2017 Sportscoach 407FW.
• The Hot Water Heater is a ATWOOD GC10A-4E 94018 10 GALLON HOT WATER HEATER GAS/ELECTRIC
• The heater has been working fine ever since we have been on the road beginning June 9th.
• Suddenly, no hot water starting yesterday.
• The unit does not work on either electricity or gas.
• We are on perfectly clean shore power in RV Park, no low voltage (I have a Hughes Autoformer) .
• Everything else in the coach seems to be working just fine.
• I have cycled the 110 Circuit Breaker.
• I have checked the 2-amp fuse on the control board for the heater unit and it is not burned out/shorted.
• I cannot locate any other "labeled" 12-volt fuse.
• I have checked the propane and the tank is full, valve is open (wouldn't explain why not working on electricity anyway)

So, how does one actually check/confirm a thermostat issue, I mean to absolutely confirm it besides just replacing it to see of it suddenly starts working again?

Regards,
One stumped RV'er

[RandK-M]

The T-stat is just a normally closed switch. A multimeter across the terminals should show continuity until the water reaches temperature of 130 0r 140 degrees. Actually, on my Atwood 6 gallon water heater there are two sets of thermostats. One for 12v gas operation and one for 120v.

I'm not sure it's a T-stat issue if neither gas or electric work though. Unless the little 120v electric toggle switch on the unit is off or the element is bad. In that case, it could be a T-stat for the gas and the electric isn't working for one of those other reasons.

If it helps, here is a link to an Atwood troubleshooting guide.
Atwood Water Heater Troubleshooting

Ray

[RandK-M]

Oh, one more thing. I seem to remember some posts on here about some new units with bad control boards, but I don't remember the brand or details.

Also try reading this post I found on RVNet about bad thermal cutoffs.
https://www.rv.net/forum/index.cfm/f...print/true.cfm

Ray

[brad10281]

Mine stopped working all of a sudden one day also. Turned out that the thermostat and the ECO thermostat failed which then led to the thermal cutoff tripping. You can bypass the thermal cutoff to see if you can get it to kick back on but if the thermostats are bad then the water heater will never shutoff. Just Google it and you'll be able to identify the thermal cutoff to try troubleshooting that first. Hope this helps.

[brad10281]

Just in case I wasn't clear above, do not run your water heater without the thermal cutoff in place. You can temporarily bypass it to check if it's bad, but please don't remove it and expect to run your water heater without it...It tripped for a reason. I got mine repaired under warranty and my dealer didn't even replace the thermal cutoff. I lost thermal cutoff before I took it to the dealer, I assumed they'd be smart enough to replace it...I was wrong. Picked one up from another dealer and put it back in place, as I was not comfortable operating the water heater without it.

[mmcbride56]

Originally Posted by RandK-M

The T-stat is just a normally closed switch. A multimeter across the terminals should show continuity until the water reaches temperature of 130 0r 140 degrees. Actually, on my Atwood 6 gallon water heater there are two sets of thermostats. One for 12v gas operation and one for 120v.

I'm not sure it's a T-stat issue if neither gas or electric work though. Unless the little 120v electric toggle switch on the unit is off or the element is bad. In that case, it could be a T-stat for the gas and the electric isn't working for one of those other reasons.

If it helps, here is a link to an Atwood troubleshooting guide.
Atwood Water Heater Troubleshooting

Ray

So, Thanks for tip about the continuity check, I really should have figured that out before (rusty hinges in the brain).
It does appear that the T_STAT is in an OPEN condition, no continuity, even the little alarm on my multi-meter was singing a sweet little tune.

FYI: The ECO for the gas valve is actually a "high-limit" switch that will open only if the hot water temp reaches or exceeds 190 degrees. The T_STAT which goes also goes through the control-board regulates power to both the gas-valve (and ECO) as well as to the relay that controls 110 power to the electric heating element. So a bad t-stat will stop everything in its tracks.
Another response has suggested by-passing the t-stat switch with a jumper wire just to see if the water heater starts working again. I may try this first before replacing the t-stat outright. Won't keep it in by-pass mode, just be a short test.

Thanks for the link to the trouble shooting guide!

[mmcbride56]

Originally Posted by brad10281

Mine stopped working all of a sudden one day also. Turned out that the thermostat and the ECO thermostat failed which then led to the thermal cutoff tripping. You can bypass the thermal cutoff to see if you can get it to kick back on but if the thermostats are bad then the water heater will never shutoff. Just Google it and you'll be able to identify the thermal cutoff to try troubleshooting that first. Hope this helps.

Yah, that was one of the things I looked at, but I think the thermal cutoff is fine. Appears to be the T-STAT itself, going to try one more test tonight.

Thanks.

[mmcbride56]

Originally Posted by mmcbride56

Yah, that was one of the things I looked at, but I think the thermal cutoff is fine. Appears to be the T-STAT itself, going to try one more test tonight.

Thanks.

Turns out I am completely wrong, the T-STAT works fine (gas ignites) when I take the thermal-custoff switch out of the circuit.

Tried with and without several times and it is definitely a bad t-cutoff switch.

Thanks all.

[DouglasReid]

I think there aer actually two thermostats as well. One for electric and another for gas. They are usually linked together as one unit though.

Since the problem is common to both I would look for something they both have in common. Im guessing the board or a fuse on the board.

[mmcbride56]

Originally Posted by DouglasReid

I think there aer actually two thermostats as well. One for electric and another for gas. They are usually linked together as one unit though.

Since the problem is common to both I would look for something they both have in common. Im guessing the board or a fuse on the board.

So, this is my latest update, and I will relay what I have learned.
On all ATWOOD (Dometic) DSI GAS/ELECTRIC hot water heaters, there is exactly one thermostat (brown wires) which controls when energy is applied, gas or electric ,which is fixed at 140 degrees (shut-off) and will kick on when the tank temp falls below 120 degrees or so.

Next to it is an Energy Cutoff switch (aka ECO) which is wired (red) to the control board and the gas valve. It is NOT a thermostat, it is a fail-safe "high-limit" switch that acts to close the gas value should the tank temperature exceed 190 degrees. The TSTAT and ECO are typically sold as a kit and replaced together. They look very similar but have very different functions as just explained.

In addition to those two items, all the new hot water heaters have an additional safety item called a thermal cut-off (fuse). It is wired inline with the TSTAT (brown wires) and is a one-time use item. If blown, it will prevent both the GAS and ELECTRIC energy from coming on. This is the item that is the root-cause for my heater to stop working. Once blown, it needs to be replaced with a new one only after assessing what casued it to blow in the first place.

The documentation from the Atwood troubleshooting guide states that this blows when a fire condition from a blocked flue or u-tube exists or low gas pressure that potentially creates a flame that is not contained with the burner. This safety item is thus designed to prevent a serious propane fueled fire.

Personally, I think this is a design flaw as I see no reason to have the ELECTRIC function stop working if the fire is a result of GAS usage. Seems to me you would put the thermal cutoff fuse on the red-wire going to the ECO and not the brown wire going to the T-STAT (not that I am a safety engineer or anything).

Alas, I am thankful for all who responded on this thread and the Good Sam forums as well. It was all very helpful and enlightening.

I do think it quite interesting that Dometic has compiled a list of the top most frequently requested replacement parts, and the DSI/TSTAT&ECO combo kit (p/n 91447 - amazon link) and the Thermal cut-off kit (p/n 93866 - amazon link) are in the top three!

You can purchase either or both on Amazon.com for a reasonably price, so you all may want to keep some spares if you have these Atwood dual fuel DSI units in your RV.

Regards,
Mike M.

[mmcbride56]

Originally Posted by mmcbride56

So, Thanks for tip about the continuity check, I really should have figured that out before (rusty hinges in the brain).
It does appear that the T_STAT is in an OPEN condition, no continuity, even the little alarm on my multi-meter was singing a sweet little tune.
...

I wanted to make one last comment here regarding the continuity check. It seems that in the case of my particular multimeter (sears craftsman), the alarm will sound when the resistance is under 30 ohms. I noticed that the initial reading was around 25 ohms or so and then decreased until it eventually hit 0 ohms indicating an open circuit. Since later testing showed that the T-STAT was functioning properly, I was a little puzzled about this continuity test "failure".

Now, I am no electrical engineer, but I do have some experience with electronic circuits. So my take on this is that even the very small current applied by my multimeter was enough power to the temp sensor circuit to mimic heat rising in the hot water tank, although rather rapidly, what started as a closed circuit condition progressed to an open condition as I performed the continuity check.

In conclusion, I would not recommend using purely a continuity check to see if your TSTAT is bad. Instead, as in my case, simply remove the thermal cut-off fuse (if you have one) from the brown-wire circuit and see if your burner ignites. If it does, your TSTAT is probably ok, although you may want to insure that it shuts off the gas once water hits 140 degrees or so, if it stays on past the cut-off point, then it probably is a bad TSTAT. Finally, if your burner still does not fire up, try by-passing the T-STAT altogether with a jumper wire between the two brown leads. Then if the burner comes on, it definitely is the T-STAT and maybe even the Thermal cut-off (but you can test that by adding the little guy back into the jumpered circuit to rule it out as well).

That, in the end, is how I was able to isolate my problem and resolve it.
Thanks again, great forum, great people!

[RandK-M]

Glad you got it all figured out. I don't think i have those thermal cutoffs in my suburban water heater and I do have two sets of thermostats. Probably a good idea for those that do to keep a spare on hand.

Ray