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Why would the blower keep running?

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  • Why would the blower keep running?

    A customer has two power vent water heaters piped in series. Not needing that much hot water, we switched off the gas valve/control panel to the first heater. I came back a while later, and the blower was running. Water was cold...I unplugged the blower. I believe these are bradford White from the late 1990's.

    Just curious.
    Last edited by NorthernIllinoisPlumber; 07-25-2009, 07:38 AM.

  • #2
    Re: Why would the blower keep running?

    I would say that both should run. If only one runs the path of least resistance for the exhaust may well be to come out the other blower and into the house instead of follow the pipe outside
    If you disconnect the blower, cap the pipe

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    • #3
      Re: Why would the blower keep running?

      They are vented seperately. Even if they were tied in...the draft should pull it out. Like the furnace/water heater vents.

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      • #4
        Re: Why would the blower keep running?

        If you didn't unplug the heater, the fan will still have power. The thermostat (I believe is surface mounted?) will send a signal to the blower to come on. Only when the fan proving switch is activated, the blower sends power (24v) to have the main burner come on.

        By turning the switch off, all you did was stop the voltage from reaching the control board.

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        • #5
          Re: Why would the blower keep running?

          Ok, I understand. As of now, she has 75 gallons of cold storage!

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          • #6
            Re: Why would the blower keep running?

            MMMM yummy NHM loves Legionella.

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            • #7
              Re: Why would the blower keep running?

              would Legionella be an issue when the heaters are piped in series? seems like since there would be flow through the first heater everytime a tap was turned on to hot, the water wouldn't sit still very long.

              piped in parallel with the cold valve off on the extra heater, then yeah I could see it.

              "fill me in if I'm wrong, I'm learning."
              No, it's not rocket science, it's plumbing and unlike rocket science it requires a license.

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              • #8
                Re: Why would the blower keep running?

                My understanding of Legionella is that it exists everywhere but fluorishes under the right conditions. Legionella is resistant to chlorine used in our water supply. A tank full of room temperature water I would think would be a 'right' condition. Once the water travels into the second tank to be heated (over 120 degrees) then that would kill off the Legionella

                My advice would be to drain and isolate the primary tank during summer months to prolong it's lifespan.

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                • #9
                  Re: Why would the blower keep running?

                  Legionella likes warm water, not hot..not cold. This is from wikipedia:
                  Temperature affects the survival of Legionella, as follows:
                  • At 60 °C (140 °F) - Legionella dies instantly - pasteurisation occurs.
                  • At 55 °C (131 °F) - 95% die
                  • 50 to 55 °C (122 to 131 °F) - Can survive but do not multiply
                  • 35 to 46 °C (95 to 115 °F) - Ideal growth range
                  • 20 to 50 °C (68 to 122 °F) - Growth range
                  • Below 20 °C (68 °F) - Can survive but are dormant, even below freezing
                  From published Health and Safety Executive guidance for employers in the United Kingdom[14]
                  The above data are recognised industry standard ranges within the United Kingdom, taken from ACOP L8."


                  If the tank is cold enough there really is not a problem especially if the tank is flushed out before using and then heated to operating temperature of 130-140. But I bet you need to be careful in the southern states where the heaters may be in the garage and subject to warmer temperatures (both water temp and ambient temp) then we have up here in the North country.
                  Last edited by APHCO; 07-25-2009, 12:22 PM. Reason: correct wording

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                  • #10
                    Re: Why would the blower keep running?

                    The tank is piped in series so the water is being withdrawn and purged and is not stagnant. She is on a well, where temps are low, but the heater is in the basement where its at least 75 degrees. But the water heater is set to 120. Does legionella only grow in dormant water?
                    Last edited by NorthernIllinoisPlumber; 07-26-2009, 07:05 PM.

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                    • #11
                      Re: Why would the blower keep running?

                      So if the chart is correct, then all water heaters should be set to 131 degrees or above. Just about all are set at 120 degrees. So every hot water heater could be at risk.

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                      • #12
                        Re: Why would the blower keep running?

                        This was discussed pretty well awhile back.

                        While Legionella is a real thing produced under the right conditions, there are literally hundreds of thousands, if not millions, of water heaters with temps below the threshold to keep the bacteria from being produced and kill it.

                        So is that not also science enough to prove otherwise?

                        J.C.

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                        • #13
                          Re: Why would the blower keep running?

                          how do they keep water towers safe? especially here locally where they don't treat the water.
                          No, it's not rocket science, it's plumbing and unlike rocket science it requires a license.

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                          • #14
                            Re: Why would the blower keep running?

                            So the blower came on as step one in firing sequence, with no gas, the blower would keep going until the board timed out because of no gas/ no flame, flame sensor never makes to open burner valve.
                            ANYONE CAN TAKE THE HELM WHEN THE SEA IS CALM.

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