My water heater sits happily, with the pilot light on, never kicking in no matter where I position the dial that specifies what temperature I want. Obviously, I’m getting cold water out of my hot taps.
Is it worth replacing the thermal coupler on it to see if that fixes it? I’ve replaced thermal couplers on furnaces - is it harder on a water heater?
Any tricks I need to know?
Thermal coupler? Is that anything like a thermocouple?
And yeah, bad thermocouples are common on water heaters, and if you can get one, you can replace it pretty easily. (I’ve only had the problem once, and I watched a plumber do it)
I replaced mine a few months back and it was fairly easy. On my model, I had to [ol]
[li]Drain the tank[/li][li]Turn off the gas[/li][li]Disconnect the gas fitting[/li][li]Remove the thermocouple[/li][li]Put the new one in[/li][li]Reconnect and turn on the gas[/li][li]Refill the tank[/li][li]Light the pilot light[/li][/ol]
Yeah, some dilletantes pronounce it “thermocouple.” 
Thanks - I guess it’s worth a few bucks before I call somebody.
Another possibility is that the “draw tube” (the tube the hot water comes out of) has dissolved to the point where it’s too short to get to the bottom of the tank. Therefore, the water coming out of your tap is cold, but the water at the bottom of the heater (where the thermostat is) is nice and hot. This one is fairly easy to check – just turn the drain tap at the bottom and draw some water out. Check whether it’s hot or cold. If it’s cold, it’s probably the thermocouple, if it’s hot, it might be the tube.
Thanks - I’ll do that too.
Right now I’m waiting for my wife to call me back to tell me the model heater we have so I can see what else I can find out.
Most water heaters are supplied with a high temperature resistand PLASTIC DIP TUBE that supplies the cold water to the bottom of the tank.
IF the dip tube should happen to fail (most unlikely) and the thermostat is working the tank will heat the water ovenight and the cold water pipe outlet at the top of the tank will be HOT.
Bottom Line: If the water output is COLD, the pilot light works, the thermostat is the first suspect. Gas control valve second and you should get a qualified technician.
:smack:
Correction: There is no such thing as a “draw tube.” Hot water is drawn from the TOP outlet of the tank!
The “Dip Tube” supplies the cold water suppy to the bottome of the tank where it is heated and rises setting up circulation to heat the entire contenst of the tank till the set temperature is reaches.
Hot water rises, Cold water sinks.
Okay, okay! It’s a dip tube. :smack: However, if the tube doesn’t go all the way to the bottom of the tank, then the cold water sits on top and the hot water stays at the bottom, which was my original point.
And failure isn’t all that rare. I had two fail on the same tank. Apparently the industry switched plastic compounds for a few years and the new compound failed frequently until manufacturers switched again.
Hot water rises, Cold water sinks.
At 4° C pure water has a specific gravity of 1.0000
At 40° C pure water has a specific gravity of 0.9922
At 60° C pure water has a specific gravity of 0.9832
Ever see an small back yard pond frozen over in winter with fish swimming on the bottom. This is a special case, since water has its maximum density at about 4 degrees C. slightly above freezing. Hence the 0° C ice is on top.
If the pilot stays lit, the thermocouple is OK. If the main burner won’t ignite, the trouble is with the thermostat or the gas valve.
Time to look at the water heater and evaluate - if it’s say, 5 years old, it’s probably worth having someone come in to check it out and repair the thing. Over 10? You’re likely to be better off replacing the whole heater.
I’m not disagreeing with physics, but this is an issue of engineering.
If you’re drawing hot water from the top of the tank, and the dip tube is broken near the top of the tank, the cold water will come in at the top of the tank and be drawn off immediately, without having the chance to sink to the bottom of the tank.
All I’ve ever been trying to say is that the problem may be inside the tank, rather than the thermostat or the thermocouple. It happened to me twice on the same tank.
Right you are. Let the tank set an hour or even overnight, and there will be a tank full of hot water. As you attempt to draw hot water the cold water will short circuit and the HW faucet will deliver cool or only warm water.
With regard to the OP it is most likely a failed thermostat.
Some HWH Repair and Maintenance Information