I have a Raypak P-R406A-EN-C pool heater, I believe the previous owner put it in about 3 years ago now. If I set the pool temp to say 84 degrees the heater fires up and starts heating, it might say the water temp is 80 degrees. It starts heating and then goes to no demand when it hits 84 degrees. The problem is the pool is maybe high 70's at best. It's as if the heater thinks the water is warmer, so it goes back to no demand. Is there a temprature sensor or something that might be causing this that either needs to be set to the current actual water temp, or maybe needs replacing? Also is there any maintenance I should be doing on this unit, such as filters, or something to wash out? Thanks in advance.