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Fan Control Center to Boiler wiring

Some background info:

I have a boiler with 3 zones.   The first zone tstat and circulator are wired to the triple function aquastat (L8124A).  Second zone tstat and circulator are wired to an Honeywell R845A (1 - Zc from L8124A, 2 - Neutral, 3 - L1, 4 - Circulator, 5 -L1, 6 - Zr on aquastat).

The third zone is a hydroair system that handles both heating and cooling.  There we have wiring as follows: W and C from fan control (which is wired to thermostat) goes to a 24V relay which in turn connects T/T on another R845A (1 - Zc from 8124A, 2 - Neutral, 3 -L1, 4 -Circulator, 5 -L1, 6 -Zr).   I realize there is the potential for the fan running while the circulator is for the 3rd zone is not on, but since this boiler does not handle my domestic water, this should not really happen.

The problem:

One of the controls for my 3rd zone is bad.  The circulator for the 3rd zone is sometimes running when the thermostat is not calling for heat.  I have verified that there is in fact no power to W/C coming from the fan control.  It appears that the relay in either the separate 24v relay or within the R845A is sticking (these both appear ancient).  Instead of replacing one (or both of these), I wonder if there is a newer control that will take their place.   Any suggestions on what control I should use?  I do not want to rewire my entire system, just this 3rd zone (the fan control is about 40 feet away from my boiler in a crawl space - rewiring would be a pain).


  • eddie_diy
    eddie_diy Member Posts: 2

    Sorry.. i may have swapped wiring of 4 & 6 in the R845A controls.  At work, can't check right now.
  • Tim McElwain
    Tim McElwain Member Posts: 4,593
    I assume this is being used

    on an oil boiler, is that correct? If so and you are no longer getting domestic hot water from the boiler the wiring could be changed.
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