The spa is aprox 9 years old. And I know it is in need of a new cover. Thinking that this was the problem with the heat, But now there is a constant noise coming from the area where the pressure switch is housed.
Do you think it would be worth it to just replace the $25 part or should I call in the experts? And, of course, get the new cover.

Not heating above 95 is typically related to a bad heater element. Of course you could have a flow issue or defective pressure switch that would cause the heater not to get power as well. You didn't mention any type of control system or if you are getting any error messages (if digital) or otherwise...

Thank you for your quick response. I am not getting any error messages. And I apologise for not understanding what you mean by the control system inquiry. Would the heating element cause the noise? I realize I could have more than one problem.