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obscenic's avatar
obscenic
Explorer
Mar 18, 2013

Atwood furnace shuts down after first failed ignition

Furnace: Atwood hydroflame 7912. Probably a 1983. The board has been replaced with a dinosaur board with fan control.

I have a very bizzare problem, that I'm hoping someone out there might have some ideas about. I've spoken at length to technicians from dinosaur boards about it with no outcomes. Here is what happens.

My furnace will run fine for many days, through many cycles. Then, with no changes to anything else (usually in the middle of the night or early morning) the following happens:
1. Thermostat turns on
2. Fan turns on + sail switch engages
3. Propane valve opens and igniter strikes
4. Furnace immediately shuts down and turns fan off
5. My programmable thermostat loses all of it's programming, time, date etc.

...There are no re-try attempts (there should be 3)

6. The furnace will remain off until the thermostat is turned off altogether for at least 60 seconds. Then there is a barely audible click and I can try again to turn the thermostat on.
7. Turning the thermostat on causes the exact same thing to happen.

To workaround this, each time this happens I remove the ignitor, blow air into the combustion chamber to clear out the propane build-up, reinstall the ignitor, turn the thermostat on, and it ignites just fine.

It seems at first glance as if there's two issues at play here (1. failure to ignite and 2. immediate shutdown) but I'm not totally sure it is two separate issues. I think if the blower wheel was allowed to run (as it is supposed to after a failed ignition) and clear out the propane it would probably ignite the second time.
  • ibyers's avatar
    ibyers
    Explorer
    Mar 18, 2013
    Maybe its the thermostat. Do you have a analog one you can try? if not I have the old one from my unit I can give you (I'm in Calgary)
  • obscenic's avatar
    obscenic
    Explorer
    Mar 18, 2013
    I'm fairly sure last time it happened I disconnected the thermostat, waited until the relay clicked and then shorted the thermostat wires together and it still did the exact same thing.
  • Old-Biscuit's avatar
    Old-Biscuit
    Explorer III
    Mar 18, 2013
    Typically IF blower is shutting down at same time burner shuts off it is either due to bad/incorrect wiring or faulty relay.
    You have a new Dinosaur board (with relay) so the board should be good

    You stated that:
    5. My programmable thermostat loses all of it's programming, time, date etc.

    I think your problem is the t-stat and/or wiring from t-stat to circuit board.

    Could be the relay connections on board or connectors for power to board but I would check wiring/terminals on t-stat and to board.
  • obscenic's avatar
    obscenic
    Explorer
    Mar 18, 2013
    Old-Biscuit wrote:
    Typically IF blower is shutting down at same time burner shuts off it is either due to bad/incorrect wiring or faulty relay.
    You have a new Dinosaur board (with relay) so the board should be good

    You stated that:
    5. My programmable thermostat loses all of it's programming, time, date etc.

    I think your problem is the t-stat and/or wiring from t-stat to circuit board.

    Could be the relay connections on board or connectors for power to board but I would check wiring/terminals on t-stat and to board.


    I misspoke in my first post: the old relay is still used - but the board is wired to do fan control. (http://www.dinosaurelectronics.com/Instructions/Fan50PP_inst.pdf - see Upgrading Older Furnace on page 1)
    The relay still cuts power if the sail switch isn't closed, or the hi-limit switch is open. It also still delays the fan on start up.

    The wiring from the t-stat to the unit is brand new. Wiring on t-stat side is good, wiring on furnace side is good.
  • D_E_Bishop's avatar
    D_E_Bishop
    Explorer
    Mar 18, 2013
    To me it sounds a lot like the board is failing. I was just wondering where you hear the faint click. I assume it is on the board and not a relay in the thermostat.

    I'm sorry, I didn't see old-biscuit's post and your reply before I made my post. I'm going to need to prind this out and read it with a pencil in hand to make sure what's happening. I do that and see if I can figure out anything not happening in sequence.
  • obscenic's avatar
    obscenic
    Explorer
    Mar 18, 2013
    D.E.Bishop wrote:
    To me it sounds a lot like the board is failing. I was just wondering where you hear the faint click. I assume it is on the board and not a relay in the thermostat.


    I'm pretty sure the click is the relay, but I'll have a closer listen next time. The board is brand new as well, it was replaced as I assumed the old DSI board was the culprit. I had the same situation prior to the dinosaur board.

    Thanks all of you for your knowledge sharing on this!
  • Old-Biscuit's avatar
    Old-Biscuit
    Explorer III
    Mar 18, 2013
    obscenic wrote:
    D.E.Bishop wrote:
    To me it sounds a lot like the board is failing. I was just wondering where you hear the faint click. I assume it is on the board and not a relay in the thermostat.


    I'm pretty sure the click is the relay, but I'll have a closer listen next time. The board is brand new as well, it was replaced as I assumed the old DSI board was the culprit. I had the same situation prior to the dinosaur board.

    Thanks all of you for your knowledge sharing on this!


    Old problem....new board didn't correct.

    "The wiring from the t-stat to the unit is brand new. Wiring on t-stat side is good, wiring on furnace side is good"......OK but is the t-stat any good
    And you are still using the old relay.

    Again..typically blower shutting down same time burner shuts off is due to bad/incorrect wiring OR bad relay.

    You are loosing power at/to t-stat (loosing program/time/date etc.) so either new wiring has a scape on insulation and is grounding out, a loose wire nut, poor connection OR old relay is faulty.
  • obscenic's avatar
    obscenic
    Explorer
    Mar 18, 2013
    Old-Biscuit wrote:

    Old problem....new board didn't correct.

    Yup, exactly.

    Old-Biscuit wrote:

    OK but is the t-stat any good

    Brand new
    Old-Biscuit wrote:

    You are losing power at/to t-stat (loosing program/time/date etc.) so either new wiring has a scape on insulation and is grounding out, a loose wire nut, poor connection OR old relay is faulty.


    T-stat doesn't get power from wires, it has batteries. There's only two wires going to t-stat; t-stat just opens or closes them to connect 12v back to the furnace.
  • Old-Biscuit's avatar
    Old-Biscuit
    Explorer III
    Mar 18, 2013
    obscenic wrote:
    Old-Biscuit wrote:

    Old problem....new board didn't correct.

    Yup, exactly.

    Old-Biscuit wrote:

    OK but is the t-stat any good

    Brand new
    Old-Biscuit wrote:

    You are losing power at/to t-stat (loosing program/time/date etc.) so either new wiring has a scape on insulation and is grounding out, a loose wire nut, poor connection OR old relay is faulty.


    T-stat doesn't get power from wires, it has batteries. There's only two wires going to t-stat; t-stat just opens or closes them to connect 12v back to the furnace.


    Then why do you loose programming on t-stat?
    5. My programmable thermostat loses all of it's programming, time, date etc.
  • obscenic's avatar
    obscenic
    Explorer
    Mar 18, 2013
    Old-Biscuit wrote:

    Then why do you loose programming on t-stat?


    At best guess I would say it's getting a shock down the line. The programmable thermostat is removable, it has pin connections to the backing plate which is where the t-stat wires connect. I can take the t-stat off it's backing plate, and leave it sitting on the counter for 3 months and it still displays the time and maintains it's settings.

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