Ndfhotub

Hello, I got this hottub for basically free and am trying to figure it out. It is set up as 115V. Everything seems to work except the heat (pump and jets all seem fine). Both boards look OK with no signs of shorting or burns. The previous owner replaced both boards not to long ago (I’m told). “D9” on the heater relay board was blinking red, and the only light on that board (no green lights) so I soldered the heater relay board as mentioned above before ordering a new relay board hoping to save a few bucks but it appears still not to be working. I ended up ordering a new board and upon setting up the new board I realized the previous owner must have replaced the board and didn't place the “jumpers” in the correct spots, so I placed them in the correct spots and plugged it back in. I now have a solid green “R18” but “D9” is still blinking red. I can’t tell if the heater is actually working though. I also checked the voltage and it looks good. Is there any indication I can look for to see if the heater is actually working? Should it be warm to the touch? Any leads I can check? Should the heater have any noise or anything? After doing some research on this tub it looks like it definitely has its flaws and if i knew I probably would have looked elsewhere, but i have a lot of time already invested in it so any and all help is much appreciated! Thank you in advance!