Profilux stand alone doser problem, doser does not stop,,,

[Rice Reef]

I am currently running a profilux standalone 3pump doser and it is about a year old. For some strange reason the 3rd pump is now constantly running and not stopping. I have disconnected the doser several times but each time I reconnected the power the same doser would be running. I have checked the settings and there are no changes and the other two dosers are working accurately. This had just started while I was cleaning out the sump... The doser is sitting far enough away from any possible water spills etc... and I have checked all the lines and tubes for each doser...

Has anyone experienced this and any idea to fix it?

Thanks

Wayne