Quote:
Originally Posted by Shane826
Rick- Isn’t a short in the water heater an issue on the 120VAC side, whereas the fuse would be 12VDC?
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Yeah, my previous post was about 120v and the resulting circuit breaker reset.
But 12v can blow a fuse, if it has a short circuit on its way to the gas valve and igniter (or if those units have failed internally).
The first place for a failure is at the TM interior switch. (It is lighted, and includes a ground connection). It is possible for the switch itself to provide a connection to ground in some modes of failure.
Step 1: pull all 3 wires from that lighted switch under the sink (taking note of which wire is which). Put in another fuse. If the blows immediately, then the short circuit has already occurred within the 12v wire from the fuse panel into the switch. If the fuse does not blow, proceed to step 2.
2) Before re-assembling the switch or turning it on, verify the 12v "hot" wire has no connectivity (infinite resistance) versus the ground wire. Then re-assemble the switch with just two wires - the ground wire and the 12v "hot" from the fuse panel If the fuse blows (even if "off" position), replace the switch.
3) Next, turn the switch "ON". (It still has only two wires, the 12v "hot" and the ground). If the fuse blows with no downstream load connection, replace the switch.
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If it wasn't the switch, it's gonna get messy. (and I might not be exactly right about this, I'm doing it from memory with the TM "down" for winter).
At the upper left of the outside face of the suburban unit (underneath a cover where the one of the screws is hard to get at) the DC thermostats are on the right side of the assembly, the AC thermostats are on the left.
The 12v DC main comes into the "safety" upper thermostat, and you may disconnect that wire. Check the wire end for less-than-infinite resistance to "ground" (the bare case of the water heater itself) -- if you don't have INFINITY, there is a short in the long and somewhat hard-to-get-at wire leading from the switch into that upper DC thermostat.
If that wire was OK, then you can plug it back in. The lower thermostat output wire (the lower thermostat does all of the normal switching between about 110F and 130F) connects the gas valve unit, check that wire and pull that lead (so that it doesn't touch anything). Now go back inside and turn the switch "ON". If the fuse blew, then THAT wire (from the running thermostat to the valve assembly) is bad and needs to be replaced. But if the fuse stayed OK, and you measure 12V on the end of that wire, then the problem is likely within the gas valve unit or the igniter's power supply.
You can verify that the 3 other wires all look good, but possibly need a service manual to proceed further. I'm hoping that it's merely the TM interior control switch gone bad!
At the lower left, multiple wires enter and exit the gas valve, with two wires
First check that no continuity exists on TM's DC wire going to the upper thermostat versus ground (the blank metal case of the water heater).