This PID allows two different kinds of control. The first is based on a set temp setting. Use it that way for your HLT. When you're ready to boil, switch power over to your BK element and switch the PID to manual mode. The probe can stay in the HLT because in manual mode the PID will control the BK element by adjusting it's power based on percentage. It won't really use the temperature feedback from your HLT probe when in manual mode. The probe just needs to be hooked up so it'll function, but it will be adjusting the BK element based on the percentage it's set to. Set it to 100 percent until you get it boiling, then adjust down as necessary-say 60 percent depending on how it works for you. Just use a regular thermometer if you want to keep track of your BK temps while your coming up to a boil and adjust power as needed.