Do you have a 0-12v signal generator? I have used one before to imitate the signal and see if pump runs, although you may need a scope as I thinks this is pulsed signal rather than constant?
https://cms.media.wilo.com/cdndoc/wilo189132/4259770/wilo189132.pdf
http://cms.media.wilo.com/cdndoc/wilo429191/4683951/wilo429191.pdf
The second link is defines the fault you have as a poor input PWM signal.
The first link is a definitive installation guide to their pumps.
The ku I suspect...
https://www.evikon.eu/competences-comp-1043/temperature-measurement-comp-1044/surface-sensors-comp-1200/pipe-surface-temperature-sensor-p-480
Something like this?