[Shop-talk] water heater troubleshooting

[scott.hall at comcast.net]

so you think I should or should not replace the thermocouple?  I'm looking at the main burner and it's not firing at all, for whatever reason, but the pilot is on and seems fine.  I believe the thermocouple should be in the pilot flame, right?  as in it's got to be hot to work, right?

can/should I shut off the gas and disassemble the main burner to see if it's clogged?  I don't know what else might be up with the heater, but the burner is definitely not coming on, and it's not getting gas because I spent a good chunk of today trying to light it manually with a match.  the gas is not getting turned on to the burner.  can I jump the thermocouple inputs to see if it turns on the gas to the main burner?

I ask (as opposed to just replacing it) because lowes and home depot here each have one thermocouple (the same kind) that is a different brand than my heater and the people at both stores were evasive about whether it'd work on mine.  before I start taking things apart or scouring the planet for one that fits my heater I thought I'd try to get smart for once and see if it's worth it.

if it's not the thermocouple or something in the 'thermostat' box that's easy to fix this thing gets a dirt nap, but I'm really hoping to get it working tomorrow--we're under tropical storm fay right now and cold showers are getting old already.

 -------------- Original message ----------------------
From: "David Scheidt" <dmscheidt at gmail.com>

> Right.  The thermocouple is a flame proving device.  It's heated by
> the pilot, and produces some current when hot.  That allows the gas
> valve to stay open. Lack of hot water is caused by the burner not
> heating the water.  it can fail to do that because the thermostat is
> set low, broken, or set to the pilot only setting.  It can also happen
> because the burner doesn't work -- clogged, blocked orifice, etc.
> 
> There are other causes of no hot water.  I've seen the dip tube that
> supplies cold water to the bottom of the heater fall off.  That means
> the replacement water is supplied at the top of the tank, and
> immediately drawn off.  The burner never fires, because the water at
> the t'stat is hot.