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  1. #1
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    SOS -- New hot water heater takes out my furnace

    First--the subject sounds crazy, I know. Second--it's a long story; bear with me. That said, on 11/14/17 I had a new hot water heater installed (Bradford White RG1PV40S6N). It replaced a similar (40g, gas, 40k btu, power vented unit) that had been in-place since 2006. Shortly after install, I noticed my furnace, original to the house (Carrier weathermaker 9200 80k btu) began to short cycle and sometimes shutdown all together. I started small & cleaned the flame sensor--it didn't solve the problem. It was throwing a 31 code for pressure. So I unplugged all the drains & the condensate trap--it didn't solve the problem either. I pulled a drain to the inducer while running and water drained fine. The pressure switch was fine too, but I still replaced it "just to see" and the problems continued. So I put the old pressure switch back on.

    For days, the furnace would run intermittently, while the water heater operated fine. Interestingly too, on two occasions, while the furnace was going through its pre-ignition sequence, the water heater also called for heat. Both times, when the water heater kicked on, it knocked down the furnace. I couldn't believe it. But it got me thinking that there could be a connection. I made sure the water heater was plugged into a different circuit (to eliminate an electrical issue), but the problem persisted.

    Fast forward to Saturday (12/2). The furnace ran all morning fine. About 11am, while the furnace was cycling, the hot water heater came on & the furnace went down immediately. At that time I decided to unplug the water heater all together--to remove it from the equation entirely. Problem was the furnace never came back on. (It did though, continue to throw the pressure code, and try to reignite after lockout--as its done through all of this--it just wouldn't fire.) So on Sunday morning, I plugged the water heater back in. ...At least I'd have hot water.

    It wasn't until Monday (sometime during the day while I was at work) that the furnace came back online. I went downstairs immediately and unplugged the water heater. That was Monday 12/4 at 6pm. And as of this morning, 3 days later, I still have consistent heat--albeit no hot water.

    I have had two techs out, and neither can isolate the problem. Like I said, all drains are clear, combustion/exhaust flues are clear. In fact, early on we thought maybe combustion air, so we removed the cover to the fire box on the furnace. It remains off.

    What is happening here? This is what I know. A hot water heater was replaced, and my furnace started failing. (Zero problems before the water heater.) After days of troubleshooting, I finally unplugged the hot water heater all together, and since doing that, I've had uninterupted heat.

    I can't bring myself to plug the water heater back in because odds are, it's going to knock down my furnace. And there's no telling when the furnace will come back. And it's cold here in NY now.

    Also worth noting, while the furnace throws the pressure code...99%+ of the time, its thrown 21 (gas lockout) two times during all this.

    Last. The furnace and water heater are side-by-side in an open, newer basement. The only thing common to them is a gas line. The water heater is downstream of the furnace on the gas line. The line they share is a 3/4" supply, that T's off and reduces on its way to each appliance. (The gas serves a furnace, water heater, kitchen stove, and dryer. And incidentally, my gas dryer & furnace work fine while running in tandem. But, I realize the dryer draws significantly less btus than the water heater.)

    Many thanks in advance for any ideas!

  2. #2
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    Dec 2017
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    Thread Starter
    BTW. I should have said, I made sure all the drains were clear, instead of "unplugged."

  3. #3
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    Aug 2002
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    Where is the installing contractor? Why are you messing with it, that's there in warranty job!

  4. #4
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    Dec 2007
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    Pressure switch code is unrelated to gas pressure code.

    Why are you not calling original installer back?

    Photos of the install.
    Model number, and serial number, of the equipment, furnace and water heater.
    The Food Stamp Program, administered by the U.S. Department of Agriculture, is proud to be distributing the greatest amount of free meals and stamps EVER.
    Meanwhile, the National Park Service, administered by the U.S. Department of the Interior, asks us to "Please Do Not Feed the Animals". Their stated reason for this policy "... the animals become dependent on handouts and will not learn to take care of themselves."
    from an excerpt by Paul Jacob in Sun City, AZ

  5. #5
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    Aug 2009
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    Beatrice, NE
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    What kind of water heater, what is the BTU input and what is the input on the furnace? It sounds to me like the water heater is pulling the gas pressure down enough to not let the furnace operate correctly.

  6. Likes STEVEusaPA liked this post
  7. #6
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    I did contact the installer late last week and made him aware. But at that time, I hadn't been able to draw a clear connection to the water heater. Now that it's been off for several days and there's been heat--I'd say it's fair I've proven the theory out. Before I call him back in, I was hoping to get some other opinions re: what could be root cause--being such a strange problem and all.

  8. #7
    Join Date
    May 2000
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    Indianapolis, IN, USA
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    They didn't vent the WH into the furnace PVC vent?

  9. #8
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    Dec 2017
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    Thread Starter
    No, they vent independently & through different walls of the house.

  10. #9
    Join Date
    Mar 2013
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    Billington Heights, NY
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    Sounds like a fuel pressure problem. The code thrown by the furnace is an odd one because it's not directly related to fuel pressure. But I can say that I have heard of other odd codes being thrown for unrelated problems, too.
    Experience - knowing when to get the hell out of the way and plug your ears. "Don't be a sissy. Turn it on!"

    Poodle Head Mikey - "the world is well populated with the unknowing and the uncaring and the stupid."

    Jtrammel - "I’m going to sell hvac systems derp derp derp"
    BBeerme - "every time he opens his mouth, he reminds me of a cow without the fart bag."

  11. #10
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    Jul 2013
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    Richmond, VA
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    I don't think they're related. Best to have a professional take a look.

  12. #11
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    Dec 2017
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    Thread Starter
    Thank you all for your input. To those that have inquired about the specs:
    Water heater is a Bradford White; 40k BTU; model: RG1PV40S6N serial: PF39701888
    Furnace is a Carrier Weathermaker 9200; 60k BTU (sorry, I said 80k earlier, typo). Model: 58MXA060-12 serial: 4095A04462

    It is my understanding that these Carrier's had motherboard issues.

  13. #12
    Join Date
    Mar 2013
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    Billington Heights, NY
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    how big is the gas line from the meter, to each one? Plus, what else is on the line?
    Experience - knowing when to get the hell out of the way and plug your ears. "Don't be a sissy. Turn it on!"

    Poodle Head Mikey - "the world is well populated with the unknowing and the uncaring and the stupid."

    Jtrammel - "I’m going to sell hvac systems derp derp derp"
    BBeerme - "every time he opens his mouth, he reminds me of a cow without the fart bag."

  14. #13
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    May 2008
    Location
    Missouri
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    I'm with the others, have the installer check the inlet gas pressure with both units operating!

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