Weil-McLain AquaBalance 120c issues

Matt51

My AquaBalance 120c (installed April '19) failed with code A44 (bad/disconnected temp sensor). Testing proved the sensor and connected wiring was good. Replaced control module, issue solved... for a week. The unit just failed again.

I'll put an ohmmeter on the sensor again, just to be sure, but I suspect another control module failure, and would like to get to the root of the problem. What is causing this?

The sensor (part# 640-000-036) tested in the correct range, both directly and through the 24-pin connector on the control module.

Thanks in advance for any suggestions

109A_5

@Matt51, Seems odd to me that both boards would have the same failure (although not impossible). Is it now a solid failure or intermittent ?

I would very closely inspect the flowing;

The wires to that sensor for chafes or rub through.
The crimps at the wire terminations.
(I have found crimps that look and feel good that are actually intermittently bad)
Connectors contacts and pin fitment.

If the system can be shut down, yet remain powered up you may be able to measure the DC Voltage at that sensor and other like sensors. I would expect the Voltage to be very close on the different sensors once the temperature equalizes. If the problem is intermittent while measuring the Voltage at the sensor wiggle the wires and connectors in a methodical way. Look for odd changes or fluctuations in Voltage.

Even though the sensors have different part numbers the resistance values seem the same (sensor testing chart). Maybe the mounting clips are different.

42 DHW temperature sensor
186 Return temperature sensor

Maybe you can swap sensors and see if the problem follows the sensor or the control board input.