Water Heater problems

Yes Mike but you do it professionally I gather (From the number) that makes a difference You do a whole lot more than I do

Funny I just did a service call for no heat this morning. Guess what it was.....yep thermocouple.
I think I have replaced six or seven of them this winter season on boilers and water heaters combined

ktmrfs wrote:
The construction of a thermocouple is pretty simple and one would expect them to have a long life, and they are pretty reliable, but not 100%.

Often times they haven't failed, but the real cause is a poor pilot flame or a dirty thermocouple or connector. Check that before replacing one..

That is almost exactly what i said slightly reworded.

Yes the construction is very simple. not much can go wrong save for a broken bond between the two different metals or enough "Char" build up on 'em (Crud, carbon whatever you wish to call it) that it does not get hot enough.

More likely a poor pilot due to an insect nest or some such.

But.. just because there is almost nothing that can go wrong.. Well you know Murphys law "If anything can go wrong it will" My name is Davis and as it turns out in the books Murphy's law and other reasons theings go wrong (i think it's book 2) they have Davis' corollary to Murphy's law.. yes I wrote it.. How it got in the book under my name I don't know (perhaps my physics teacher who is the first person I told of it) "If nothing can go wrong.... It will anyway".

So I do agree they can fail.. And do.

Bobbo wrote:

wa8yxm wrote:
Though as someone said Thermocouples CAN go bad. Very rare

This statement I disagree with. In my vast experience, every time that a pilot light would not stay lit, it was the thermocouple that had gone bad. That probably amounts to 3 times in my 64 years.

my exerience. In my trailer WH or house WH haven't had a thermocouple go bad. But in my house gas fireplace I've had several fail and need replacing. Output voltage open circuit was fine, but with it attached to the load, voltage dropped well below the min voltage. New thermocouple, all good again..
The construction of a thermocouple is pretty simple and one would expect them to have a long life, and they are pretty reliable, but not 100%.

Often times they haven't failed, but the real cause is a poor pilot flame or a dirty thermocouple or connector. Check that before replacing one..

And zero in my 68 years though I have had pilots go bad.

wa8yxm wrote:
Though as someone said Thermocouples CAN go bad. Very rare

This statement I disagree with. In my vast experience, every time that a pilot light would not stay lit, it was the thermocouple that had gone bad. That probably amounts to 3 times in my 64 years.

Thank you everyone! We will check all those things and try your suggestions. Thank you again!

Though as someone said Thermocouples CAN go bad. Very rare

The thermocouple is two pieces of metal bonded or twisted together They are Two DIFFERENT metals (IE: copper and aluminum or steel) and when heated generate about 0.480 Volts.. This powers an ELectromagnet inside the thermostat valve.

The magnet is not strong enough to "Pull open" the gas valve. but when you push down on teh button or do whatever it says to do that opens the valve allowing you to light the pilot.

NOW.. HOLD THAT POSE (Button) for at least 1 full mintue after the pilot is lit
THIS IS THE #1 Failure mode (Operator error) in some cases 2 minutes.

Then releast it and turn the knob to ON.

Possible other issues

Bad thermocouple (Rare but it does happen)
Bad thermostatic valve (The magnet open)
Bad connection between them

prichardson wrote:
Ensure that there is a good pilot flame and that the tip of the thermocouple is in the pilot flame. With a pencil eraser polish the contacts where it is attached to the gas valve and DO NOT over tighten when reattaching (finger tight is enough). If it sill does not stay lit it is probably a bad thermocouple.

yup. and thermocouples can go bad, generally they are reliable but can fail. good news is that they are reasonably easy to replace and reasonable cost.

Also make sure the pilot flame is good. even a tiny bit of debris in the orifice can be enough to limit the flame to a point where it won't be able to keep the thermocouple hot enough to keep the valve open. If cleaning the thermocouple doesn't solve the problem, take out the pilot orifice and clean it with a small diameter piece of wire and blow it out with a blast of air.

the gas valve protection circuit to turn off gas in the event of a loss of flame is very reliable, but also the thermocouple is a very low current output with high impedance driving a sensitive detection circuit that must run on very low current and voltage and keep the gas valve open. So, once a thermocouple has a low ouput voltage under load, the system is marginal. can be caused by a low pilot flame or dirty thermocouple or thermocouple on it's way out. Usually it is the thermocouple that fails, not the gas valve.

Ensure that there is a good pilot flame and that the tip of the thermocouple is in the pilot flame. With a pencil eraser polish the contacts where it is attached to the gas valve and DO NOT over tighten when reattaching (finger tight is enough). If it sill does not stay lit it is probably a bad thermocouple.