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Wiring up a power venter

STEVEusaPA Member Posts: 6,505
edited December 2019 in THE MAIN WALL
I always wonder about 2 things when wiring this power venter or any combustion air system, for oil in this example.
Looking at the diagram:
1. Why does the signal come from:
The burner motor on the primary to the PV control, then back to the burner motor, instead of just directly from the high limit (B1 on aquastat). Seems the way it's wired now could cause a slight release of unburnt oil into the chamber if something goes wrong with the power venter. Seems like the burner motor would slightly slow down as it turns off, but the oil valve wouldn't close immediately. Either way it's wired the primary still gives the burner pre & post purge.
2. If the signal runs from the burner thru the PV control and closes a switch, then back to the burner (series) why does it require a neutral? The PV has it's own line and neutral and ground.

Just curious if anyone much smarter than me had any insight.

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  • Ironman
    Ironman Member Posts: 7,378
    I'm certainly not smarter than you, but here's my take from the diagram:
    The limit terminal is always hot as long as the limit contacts are closed. A call from the stat (T T) does not effect that. The burner wire must be used because it's cycled by the thermostat call. The limit wire is not and if that were used, the stat would have no control of the burner.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,505
    Thanks Bob, and yes you are way smarter than me!
    Makes sense about the limit. I was specifically thinking of B1 off of the aquastat, which only gets power when there is a call for heat. So B1>PV terminal #1>PV terminal #4 to Limit on Primary Control.
    Any thoughts on the 'extra' neutral coming off the PV board at terminal #2?

    There was an error rendering this rich post.

  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,646
    I'm guessing the redundant neutral is because this could also be used for 24v operation, since the diagram is showing 115v there ends up being 2 neutrals.

    I do see your point of the oil solenoid not being wired through the control. But once the PV has proven out then and only then will it make terminals 1&4 allowing the normal sequence of pre purge and post purge.

    I really hate power venters! Oil really works best with a chimney, gas with direct vent.
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,505
    edited December 2019
    Thanks, @Solid_Fuel_Man. I agree. This one the chimney collapsed, 100 year old house, no terra cotta liner. This was the owners cheaper and probably only option.
    Nothing like drilling a hole thru 2' of stone on a Saturday...

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