Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Eating Thermocouples

don_52 Member Posts: 199

Johnson (BASO)



The -dash_ # is length, not sure about 18".

HTH, db


  • reevesjo_2
    reevesjo_2 Member Posts: 2
    Eating thermocouples

    I have a 12 year old Haugh's G400 natural gas heater that eats thermocouples. I think Haugh's was bought out by Jacuzzi, but I can not find out for sure. It has a 3/8NPT SIT 630 Eurosit #630516 gas valve (Italy). The valve is not electric. I have replaced the thermocouple three times in the last three months, with a Honeywell Universal 30 millivolt. The last time with a LUX standard copper 18" CC0018 because the Honeywell was not available.
    Question: What am I doing wrong? It works fine for awhile and then just fails. The pilot goes out and will not start again without replacing the thermocouple.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
    Pilot flame too hot???

    I know the old saying of "They don't make'em like they used to" definately applies to thermocouplers. Was a time that you NEVER had to replace them. Now a days, everyone in the company has half a dozen at any given time. We have found that the Johnson Controls Bull Dog (?) extra heavy duty coupler seems to hold up well.

    It was pointed out to me by someone I trust dearly (Timmy Mac) that if the pilot flame is too "hard" that it can cause early thermocoupler failure. Try backing the flame down a bit. It doesn't have to look like the neutral burn of an oxy-acetylene rig...

    I'l check the brand name on the Johnson coupler. Bull Dog doesn't ring true for some reason.


    There was an error rendering this rich post.

  • Boilerpro_5
    Boilerpro_5 Member Posts: 407
    Yep, what Mark said.....

    Adjust the thermocouple so after it is in the flame for several minutes the thermocouple is only a dull, not bright red. Also the flame should only envelop the top 3/8 to 1/2 inch. Get an electric meter. Output should be 24 to 30 MV for most systems. Also look for leaks where the pilot tubing enters the pilot, if a flame is burning here it will eat the thermocouple.


    To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"
  • lchmb
    lchmb Member Posts: 2,997

    Have you tested to see at what point the gas valve is dropping out? Is it possible it's not the thermocouple but in fact the gas valve?
  • reevesjo_2
    reevesjo_2 Member Posts: 2

    Thanks for all the good, quick advice. The thermocouple did appear too red, so I backed the pressure down on the pilot. Now, the thermocouple is "not quite red" and the pilot is staying lit and the burner fires up OK when the thermostat calls. So, I will leave it here for awhile to see what happens.
This discussion has been closed.