Thermal cut off fuse

Confirmed it is not a diode, the statement in the Atwood manual is incorrect. Here's a link to the device that's used in my Atwood water heater, it's the G4 model, 98 degrees C.
http://thermodisc.com/en-US/Products/Microtemp/Documents/Microtemp_thermal_fuse_bulletin_091613.pdf

It's resistance should be less than one ohm is it's not tripped.

Wayne Dohnal wrote:
If it's really a diode it needs to be tested as a diode. Even if it's good it will read open circuit in one direction, and depending on the meter and setting, could read open circuit in both directions. Having said that, I've personally never heard before of a diode being used as a thermal fuse.

It is not a diode. The case looks like a diode case though. Inside is a metal link that melts at a specified temperature.

Per Atwood Manual:

THERMAL CUT-OFF DEVICE
Current Atwood direct ignition water heaters are equipped with a thermal cut-off device. This device is located on the incoming power wire and is connected to the thermostat. The thermal cut-off is designed to permanently break circuit and shut down the water heater before excessive heat can cause damage due to obstructions in the main burner tube or flue tube caused by spiders or mud wasps. These obstructions can cause the main burner flame to burn outside the main burner tube. When the flame or the heat from the flame contacts the thermal cut-off, the circuit will open.

Thermal Cut-Off-----heat sensing diode that cuts power to circuit board if a flame backs out of the burner tube or flue tube normally caused by an obstruction in these areas.

Thermal Cut-Off
A one shot heat sensing fuse that’s normally closed and sends power to the thermostat.
When tripped by excessive heat (190°F), (i.e. blocked burner or flue tube) it cuts power to the circuit board and shuts down ignition

As suggested.....
It can be removed from system to TEST operation of WH.
IF all other components are working correctly WH will function....t-sat/ECO/circuit board etc.

Just like a fuse.......one shot, no reset. Replace if blown.

If it's really a diode it needs to be tested as a diode. Even if it's good it will read open circuit in one direction, and depending on the meter and setting, could read open circuit in both directions. Having said that, I've personally never heard before of a diode being used as a thermal fuse.

It meter reads open circuit .

The water heater ran for about a day, then nothing, the thermal cut off is the only thing I can find right now.

jasdms wrote:
I have a atwood water heater, it will not light, not on electric or gas, I think I found the problem, the thermal cut off fuse, my question is can you run contninuty through this fuse?? I tried, it will not read on meter

When you say "won't read on meter" what do you mean?

If by "won't read" you mean it reads open circuit, then replace the fuse.
If by "won't read" you mean it reads 0 ohms, then it is fine.

As always, before you replace a fuse figure out why it blew. This is an important fuse not to bypass, because it will keep your camper from burning to the ground...

NO.....the thermal cut-off is a one shot diode to prevent fire.....it blows when temp of 190*F (+) is sensed and shuts down all 12V DC power.
Excessive temp is usually due to blow back of main flame out of combustion chamber due to dirty/blockage in combustion/exhaust 'U' tube.

As a test....disconnect thermal cut off from t-stat and lead from control board (brown wire) and connect directly to t-stat. Test water heater......then get a new thermal cut-off and clean combustion chamber (run a wire thru/tie rag on and pull back thru 'U' tube)