Hey everyone, just filled up my (new to me) used Jacuzzi j-315 yesterday, running into a little bit of issues, wondering if anyone has some insight.

Yesterday filled it up with water, turned on the power, and I was getting a FL1 code (which is a flow switch open, error). so therefor the heater would kick off immediately after coming on. Thought it was possibly an air lock, so tried blowing more water through the lines with a hose, it did nothing. So I did some testing on the flow switch itself, meter across it and I get no continuity. (there's my problem I'm guessing) so I pull the connectors off the flow switch, jump them together, and there goes away my error and the heater now stays on.

circulating pump sounded normal (to me anyways) last night, water heated up fine. but I noticed this morning the pump was a little more noisy than it was yesterday.
I can feel movement in the water coming from the circulating pump vent in the bottom of the tub. (although it doesn't feel strong, but nor did it last night. also when filling the tub I noticed there was some gunk buildup in that line, as after about 5 minutes it shot out some slime and a bit of antifreeze that was in it)

So I guess my questions are as follows:

Is this noise normal for my circulating pump? or does it sound like its being water starved? its not hot to the touch, just slightly warm. (Here is the video! j315 circulating pump - YouTube )

How would I clean out all that gunk from the lines to make sure there's no more buildup?

If I order a new flow switch, does the tub have to be drained to replace it? I never noticed any shut off valves on any of the lines.

thank you.