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Weil-McLain Aquabalance "A 16" error but outdoor sensor is connected

alesage Member Posts: 5
This is most likely going to end in a service call :) but a few questions before I get on the phone.

Starting up a new Aquabalance 120 C combi boiler, the system goes through its "FH" purging cycle but then I get "A 16" error, "Outside sensor is not connected". The sensor is connected.

I've used a multimeter to check its wiring, no resistance from point to point.

I've checked the two fuses, both are intact.

What next?

Note that the sensor is apparently optional but changing the "OTC exempt" setting has no effect.

Ultimately I probably need a service call, but do I need a special kind of technician to be able to diagnose this fault? It seems like the worst case is to replace the control board.

Should I call Weil-McLain?


  • rick in Alaska
    rick in Alaska Member Posts: 1,458
    Take the wires off the boiler and check the resistance there. You should be reading the resistance of the sensor at that point, which will be something like 8-15,000 ohms, depending on the outside temperature. If you have no resistance, then there is a bad connection, or the sensor is bad.
    Also, make sure it is connected to the right contacts on the boiler.
  • alesage
    alesage Member Posts: 5
    Just an update: the resistance of the sensor is around 16K, I do believe I'm on the right contacts. I'm going to arrange for a service call and cross fingers, will report here again, meanwhile thanks Rick.
  • Jorako
    Jorako Member Posts: 1
    Keep us posted, I came here to start my research on a replacement for my 20 year old WTGO now that we have NG in my neighborhood. The Aqua balance is high on my list.
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,646
    I like the ECO (or any of the Weil McLain fire tube) better than the Aquabalance. I find them easier to clean and setup. Many retrofits can be direct piped with a fire tube mod/con.
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
  • alesage
    alesage Member Posts: 5
    This turned out to be a "PEBKAC" moment for me, please ignore and thanks for replies all--I incorrectly believed that lockout (A-type) faults were reset by power cycling, and further was pressing "reset" for too long. Please don't kick me out of your very helpful site :smile: . Now all is copacetic with Aquabalance boiler.
  • Bouldermiah
    Bouldermiah Member Posts: 1
    How did you resolve, I am having same issue
  • GGross
    GGross Member Posts: 1,072

    It would appear that the OP solved their problem by properly resetting the fault on the boiler