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Old 08-01-2012, 02:55 PM   #1
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1987 32' Excella
Nepean , Ontario
Join Date: Mar 2006
Posts: 1,157
Hot Water Heater failure and fix

I've already solved this issue, but because it can be a common issue that can elude solving, I'm posting this.

We had been to a rally about 1-1/2 months ago and all worked well. When we got home we parked the trailer on our driveway next to a spruce tree. We headed out this past weekend to a unit rendezvous. and overnighted at a Walmart. The next morning I flipped the switch on the hot water heater and got the ignition popping noise, but it seemed a bit louder. When I got ready to wash, I found that the water was still cold and now flipping the hot water switch did nothing.

When I got to the rendezvous I took my VOM (volt-ohm-multimeter) and found that there was no 12-volt power at the hot water heater. I started checking from the breaker panel – OK power at the breaker panel; OK power at the water switch; switch works OK (on/off); OK power at the brown lead from the switch, but no power after that.

It turns out that Atwood inserts a “thermal cut off” just at that point. This is a small silver-colored cylinder with radial leads (about the size of a 1-watt resister) slipped into a clear soft plastic tube. It is attached with spade lugs. The purpose of this thermal cut off is to prevent a fire where the burner tube is blocked, as was mine, by spider webs. Where the burner tube is blocked, ignition takes place outside the burner tube, in proximity of the thermal cut-off and, like the fuse it is, it blows shutting off all power to the hot water tank controls.

Atwood sells a small package of 2 of these cut-offs with replacement wire and instructions – for the princely sum of $39.95 (in Canada, that is). The instructions tell you remove the screw holding the air shutter and to slide the shutter to one side to permit you to slip a flexible brush through the burner tube to clean out the spiders’ webs. I found that this was not possible, and in order to do this one would have to totally dissemble the burner. However, I found that using compressed air did the trick – I had a glob of spider webbing fly out the exhaust port of the hot water tank.

Attached the replacement thermal cut-off and adjusted the air shutter and the hot water tank is functioning as it should.

AIR 12148
1987 Excella 32-foot
1999 Dodge Ram 2500HD Diesel
blkmagikca is offline   Reply With Quote
Old 08-01-2012, 07:21 PM   #2
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1977 Argosy 24
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Milltown , Wisconsin
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Posts: 1,075
Thanks for posting that.

ventport is offline   Reply With Quote
Old 11-01-2012, 07:05 AM   #3
2 Rivet Member
1995 30' Limited
1995 31' Land Yacht LE
Seattle , Washington
Join Date: Aug 2011
Posts: 23
Water heater issue resolved

Thanx for the replies. An RV repair guy at a neighbors RV in Brookings OR turned to my issue when done. He determined the switch was bad and replaced just the switch - then noted the fuse at the rear of the engine cover was bad and drove to his shop for a replacement (and spares for me). Problem solved at a cost of $35. I gave him $40 in gratitude.
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Old 11-01-2012, 08:34 AM   #4
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1977 31' Sovereign
1963 26' Overlander
1989 34' Excella
Johnsburg , Illinois
Join Date: Jul 2005
Posts: 2,941
I have seen the problem a number of times and unless you have a meter there, or know that this can occur, it can be difficult to find the problem.
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