Ultraheat Tank Heater Pad Issue

As it appears you have access to the pads I will suggest a clamp-on ammeter will tell you exactly what is going on as far as what is working and how much power they are pulling. Very possible those rear pads are not getting power or it just needs to be a bit cooler. Yes the converter fan will run continuous when any of these 12v pads are activated.

I added 120v pads as I assumed I would be on utility power in these conditions.