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Outdoor reset question with Buderus GB142

I had a Buderus GB142/30 with an indirect DWH tank installed this spring.  I am just getting around to using the heat now (didn't need it in July - Ha!), and I am trying to understand what the outdoor reset is supposed to control; the boiler and the circulators, or just the boiler. 

I came home the other night, it was 70's outside, and I have the hi temp shut-off at 65 temperature.  I went into the basement, and noticed that the basement zone circulator was running - the basement thermostat was calling for heat.  The boiler, of course, was not running.  I was expecting the outdoor reset to turn off the circulators when it shuts off the boiler.  I haven't checked, but I presume that the same happens when the DHW calls for heat; that the zone cirulators still run if needed, but the boiler circulator turns off?  

So, is it ok for the zone circulators to be running while the boiler circulator is off?


I looked at the setup diagrams that came with the boiler, and the outdoor reset.  It does not apear to show a control from the outdoor reset and the circulators.

Thanks for any input


  • ChasMan
    ChasMan Member Posts: 462
    It depends

    There are a great number of ways to wire up that boiler. In its simplest form, the thermostat calling for heat should not turn the circulator on if the outdoor temperature exceeds the warm weather shutdown temperature. Do you have more than one circulator pump? Do you have zone valves? Do you have any external relay panels or other controls in the system? All of these would need to be wired in a way to get it to function as it should.
  • stuckinthedirt
    stuckinthedirt Member Posts: 21
    two zones


    I have two zone: the basement and the living area; one circulator per zone.  There is an external relay box (an Argo AR861-2II).  The thermostats and line power are wired directly to the Argo.  The line power then goes to the boiler, plus a control signal to the Buderus AM10 outdoor reset controller.  There are no zone valves.

    Is it easy to wire it to have the outdoor reset control the circulators?

    Also how much does it matter?  My heating contractor says that it doesn't matter (aside from the cost of electricity to run the circulators) and that it is even better for the circulators to run continuously.  I was concerned that the circulators are running with a starved suction if the boiler circulator is off, but my contractor says that there header below the boiler allows the water to circulate through the zone, even if the boiler circulator is off - is this correct? 
  • Ironman
    Ironman Member Posts: 7,336
    Sounds Like Wiring is Correct

    The AM10 reset control does not control circulators, just boiler water temp and warm weather shut down. There should be no need for space heating at or above the WWSD temp. Why would there be a call for heat when it's above 70 outside? The T'stat needs to be lowered to shut off the pump, or if for some reason you are cold at 70deg. outside, the WWSD needs to be raised.

    The space heating circs. are controlled by the Argo panel which turns on zone pumps as their T'stat(s) call. It also signals the boiler to fire on a heat call. The DHW circ. should be wired to the "PS" terminal on the boiler terminal board if the Buderus tank sensor is being used. On a DHW call, the boiler's BC10 control overrides the AM10 reset and fires the boiler regardless of outdoor temp. It also starts the boiler circ. and the DHW circ.

    The circs. will not be "starved" if the boiler circ. is not running: they are piped in primary/secondary fashion. What your contractor told you is correct.

    Either lower the thermostat or raise the WWSD temp. No need to re-wire.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • stuckinthedirt
    stuckinthedirt Member Posts: 21
    One other question

    Thanks Ironman,

    One other question.  I notice that there is a post purge feature on this boiler.  After the call for heat is over, the boiler circ keeps going for a set time.  However, the thermostat has shut off the zone circ.  What is the purpose of the post purge timer, if my zone circ is off, and so I can't get the heat from the boiler to where I would like it?
  • Ironman
    Ironman Member Posts: 7,336
    Post Purge Is...

    To extract as much residual heat as possible after the burner shuts off. If you had only one zone pump, it could have been wired in parallel with the boiler pump (PK) and thus would have remained on as long as the boiler pump. This function also keeps the DHW pump on when it"s wired to "PS". The time is adjustable.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
This discussion has been closed.