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Al_Fresco's avatar
Al_Fresco
Explorer
May 21, 2014

Water Heater Woes

I am having a problem with my SW6DE Suburban water heater. It runs fine on electric. Using the electric mode, the water comes up to temperature (hot, but not scalding at the kitchen faucet) as usual and stays at that temperature for hours with no water escaping from the relief valve. With hot water in the tank, if I now turn off the electric source and turn on the gas, the burner lights and continues burning without ever shutting off (as long as I have the gas turned on). The water temperature at the faucet becomes dangerously steaming hot and the pressure relief valve starts dripping rather profusely.

I checked the voltage to ground from the brown wire attached to terminal 1 of the gas valve with hot water in the tank. The voltage was zero. From what I can decipher from the circuit diagram, that wire comes from the thermostat that controls the gas valve and should have no voltage on it when there is hot water in the tank.

I am assuming that, since the gas valve is open with no voltage on the brown wire, the valve must be defective. For those of you with more expertise in such matters, am I making a reasonable assumption?

4 Replies

  • Cobra21's avatar
    Cobra21
    Explorer
    May 21, 2014
    Old-Biscuit wrote:
    You are testing for 12V DC Voltage at gas valve..correct?

    Even if gas valve was stuck open (you would hear/smell propane all the time in outside compartment) it would not light off unless spark electrode ignited the main flame....which it can't do without 12V DC power.

    Bad t-stats for propane side.......they are the ones on right under 'push to reset' cover. They are 12V DC.
    If t-stats are bad (failed close) propane will continue to burn/heat until PRV blows (210*F/150#)


    I agree with "Old Bicuit" I think the high limit (high temp.) T Stat
    is shot. If water is flowing out the pressure relief, shut it down ASAP. You know what happens if the pressure relief valve fails...Boom.

    Brian
  • Al_Fresco's avatar
    Al_Fresco
    Explorer
    May 21, 2014
    I checked for the odor of gas with the water heater gas switch turned off and the gas supply on. No gas odor was detected at the burner tube. With a tank full of hot water, the voltage to the connector that attaches to terminal 1 of the gas valve read zero. When the water heater gas switch was turned on, the voltage went to 13+ volts and the igniter started firing. Therefore, the t-stat does appear to be malfunctioning – just as you suggested, Old Biscuit. Thanks again for your help.

    Makes me wonder what would happen if this situation occurred for a long period of time in an unoccupied RV. The water supply would eventually be exhausted (by boiling out of the pressure relief valve) and the burner would continue firing in a dry tank. I would think things could get pretty hot under those circumstances – to the point of perhaps starting a fire. I know this problem will serve as a reminder to me to always turn off the heat source to the hot water heater when it is not being used.
  • Al_Fresco's avatar
    Al_Fresco
    Explorer
    May 21, 2014
    Old-Biscuit,

    Yes, I did check the 12V DC at the gas valve. Per your suggestion, I will check to see if I can detect gas odor with the gas supply on and the gas switch to the water heater off. Not sure why the voltage would be zero at the valve if the t-stat is the cause of the problem. As you suggest, the sniff test should help determine if the valve is at fault.

    Thanks for your response to my inquiry.
  • Old-Biscuit's avatar
    Old-Biscuit
    Explorer III
    May 21, 2014
    You are testing for 12V DC Voltage at gas valve..correct?

    Even if gas valve was stuck open (you would hear/smell propane all the time in outside compartment) it would not light off unless spark electrode ignited the main flame....which it can't do without 12V DC power.

    Bad t-stats for propane side.......they are the ones on right under 'push to reset' cover. They are 12V DC.
    If t-stats are bad (failed close) propane will continue to burn/heat until PRV blows (210*F/150#)

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