DC fuse blown on water pump/hot water heater

[Robert59]

I have a 2016 3605 Toy Hauler with an Atwood GC10A-4E water heater. I came home to the trailer and found I didnt have hot water. It was working without problem and has been set up for several days. I never use propane to heat water, always electric. The light was out on the switch on the control panel. A light was noted next to the "water pump" blade fuse. I have never used the water pump as I am always in a park.
I initially replaced it with a 10 amp fuse. The same as the one that blew. The water heated for a while but again the fuse blew. The light on the switch on the control panel lit up when I turned the electric water heater on. I replaced it a second time and it blew immediately. So I feel the water heater element is good.
I checked the fuses on the control panel and the fuseable link to the thermostat. Both are intact and conducting electricity.
I am going to try to get the control module checked at local dealer. The thermostat seemed loose behind the black cover. I removed it with care and the spring was not behind the keepers and a clear plastic piece appeared to have broken behind it. It is a very inexpensive item and I plan to order a replacement.
I've checked all the wires and have not found anything that appears to be a dead short. All wiring insulation is in excellent shape.
Has anyone else had this happen who could put me on the path to repair it?
Thanks for any assistance you can provide.

[sundancer 87]

You could disconnect any of the connections to the control board and see if the fuse blows again. If it doesn't then start adding one connection at a time to see if the fuse blows.
The element is 110 volt AC and is controlled by a relay on the board. A bad element is essentially an open circuit so even when bad it doesn't have an impact on the board per se.

[Robert59]

Yes I know that is what has me stumped. The breaker is fine. Its the DC side. No other problems with any of the DC fuses.
I'm going to replace the thermostat and ECO first. Then Monday have the Control module checked. No one is open til Monday.
Just seeing if anyone had the same problem.
How do I access the rear of the heater. That has me scratching my head too.

[sundancer 87]

Originally Posted by Robert59

Yes I know that is what has me stumped. The breaker is fine. Its the DC side. No other problems with any of the DC fuses.
I'm going to replace the thermostat and ECO first. Then Monday have the Control module checked. No one is open til Monday.
Just seeing if anyone had the same problem.
How do I access the rear of the heater. That has me scratching my head too.

Is the heater under the refrigerator?

[Robert59]

No its in front of the slide out for the kitchen. I cant figure out how to get access

[Robert59]

I wonder if the thermostat switch can short out. I turned off the electric switch and put another fuse in. I turned on the water pump and it didnt blow. I had the thermostat unplugged and I turned on the electric water heater and it did not seem to blow. So as I said I'm ordering replacement parts. I cannot believe how inexpensive they are.
So we will see what happens. Maybe it will fix it.

[persistent]

The installation and operation manual seem to say the 12 volt gas system is not connected to the 120 volt electric heat system. I do not see a relay in the 12 volt diagram.

According to an etrailer.com support person, Dometic GC10A-4E SP Water Heater and Atwood AT94022 are the same model under new Dometic management. www.etrailer.com.

Operating instructions indicate electric heating circuits are separate from gas heating system. Gas heating system uses 12 volts. Electric heating uses only 120 volts.

Instructions for electric heating do not reference the remote lighted switch required for gas operation. See page 4 of instructions.

Most RV water heaters I worked with use 12 volts for both gas and electric heating. This model apparently does not.

I expect the blown 12 volt fuse labeled “pump” does not affect electric heating. If it is indeed the pump, it won’t affect gas heating as well. If it is miss-labeled and includes water heater 12 volts, then it likely only affects gas heating.

Reset electric heat:
“If the manual reset high temperature limit switch should operate, reset switch (FIG 11-A) by depressing with pencil or other nonmetallic object. If still experiencing problems contact an authorized Dometic Service Center or Dometic Service Department.”
http:/www.dometic.com for service issues.

If the reset device and or the "on/off" switch is broken, that may be why electric heat does not work.

[Robert59]

Thank you for the information. I appreciate it.
I've ordered the ECO/Therm replacement packs. Worth 12.00 and as the one fell apart its a start. The "Water pump" label is a misnomer. That fuse powers the control panel water heater switches (electric and gas). It powers the board for the gray/black/water tank fills. Along with the water pump.
While I had the thermostat unplugged, I put a new fuse in and switched on the water pump. The fuse held. I can only assume the problem stems from the electric and gas water heater switches being place in the on position. With the therm unplugged, I switched on the electric water heater. The fuse held. My assumption is that this switch hopefully is the dead short problem. However I am unable to use it in that mode as the therm switch being disconnected is a hazard.
As to the fuse not interfering with operation of the water heater, I must disagree. As this is the problem. I see on Youtube videos people trouble shooting their water heaters with power. With that fuse out, I cannot get power to those circuits to troubleshoot.
As to the figure 11 in your reply showing a cut off switch, I have not been able to locate that as well. With the new thermostat and ECO coming I hope this fixes the problem. If not, I will then look at the control board.
Again, when I initially replaced the fuse, the water heater worked for a time until that fuse was sacrificed. So I feel certain, the heating element is not the problem.
Will give a follow up when I determine what the problem was.
Thanks for the reply

[leisuresolar@gmail.com]

Excuse me for butting in, but I love a good conundrum. There are a lot of twists to this problem. The water heater only uses 12V for control circuitry, and 120V (and LPG) for actual heat. However, it probably uses 12V for LPG circuitry also. And the water pump uses only 12V. But it is possible on some coaches that the water pump may shut off if the water heater tells it to, depends on how smart the coach is.

It seems to me that, for some reason, the 12V control on the water heater is blowing the 12V pump fuse. Or vica versa. A very weird problem indeed. I wonder if the 12V water heater fuse is the same fuse as the 12V water pump?

[Robert59]

Well it seems i found the fix. I can only assume the thermostat or ECO switch got a dead short in one of them. The replacement of these switches has apparently fixed the problem. I have hot water and my water pump and grey/black water meters work.
Hope this helps someone down the road w the same problem.