I apologise for the late follow up, but I have finally got everything working.

 

 

 

I checked the wiring many times but could not find any problems with it. I even went as far as to attach an RJ-11 directly to the filter.

 

 

 

Eventually I decided to just try swapping the filter, and it worked immediately with the new filter. Guess I was just really unlucky and got a faulty filter.

 

 

 

Thank you for the assistance, hopefully everything continues operating without fault for years to come.