gas water heater furnace not firing up

RatLabGuy

RatLabGuy

You look like a monkey and smell like one too
Joined
May 18, 2005
Location
Churchville, MD
~3.5 yo gas water heater. Seem to have an issue w/ the main burner not kicking on to heat the water when appropriate. Daughter used it for bath, didn't turn on, after awhile just cold water.
The pilot light is still lit.
Then after some random time, it turned on. Son just took a shower, while he was in, I went down and checked it - burner not running. Then he ran out of hot water. Furnace on it is running again now.

So I get the impression is it something between the thermostat and the gas valve.
Where to start diagnosis?
It's just started today but it seems like an intermittent thing.

I haven't drained the tank since purchase so I'll probably do that to ensure there isn't sediment buildup
 
Easy fix would be a bad thermocouple. It senses heat from pilot flame to allow gas valve to open
 
moldman05 said:
Easy fix would be a bad thermocouple. It senses heat from pilot flame to allow gas valve to open
Click to expand...
Right but the pilot is staying on all the time. If the thermocouple were bad wouldn't it keep the pilot from igniting? This is more like it's just randomly not letting the full gas on.
 
Thermostat would be my first guess
 
RatLabGuy said:
Right but the pilot is staying on all the time. If the thermocouple were bad wouldn't it keep the pilot from igniting? This is more like it's just randomly not letting the full gas on.
Click to expand...

The pilot stays lit all the time. The thermocouple monitors that the pilot is lit, and then allows the gas valve to open when the tank thermostat senses the tank is below temp. The thermocouple is a more frequent failure mode than the assembly that contains the thermostat and gas valve from what I remember.

There is a thermocouple test that involves relighting the pilot or something like that, and if the thermocouple is bad the burner will shut off or something. My memory is foggy, it's been a while since we had one of those...
 
If the thermocouple is bad the pilot won't stay lit either.

If it were mine I'd start with the thermostat
 
gas valve - my HVAC did that. order one off amazon / grainger / MSC etc and do it your self. just check it real good for leaks.
 
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