The R407A heater was installed 4 years ago as part of a complete pool remodel. It has been working fine until 7 weeks ago. When turning on the heater for either spa or pool use, the display shows it is attempting to light but after several attempts the message "water switch open" shows in the display. When this initially happened I read up on the switch info and just bumped up the pump speed to generate the necessary pressure to close the switch. This worked for about a month before even running the pump at 90% maximum flow would not close the switch. The Installation Manual states the Water Switch is preset at the factory to close at 1.75 psi. On rare occasions the heater will light but within 5 minutes it shuts off with the "water switch open" message being displayed. The heater diagnostic indicates Flame Strength = 8 Good; Supply Voltage = 27.8 V; Run Time = 350 hrs; Cycles = 972; stored faults = Hi Limit 2 Fault & Water Switch Open Fault. (Note: It is possible the Hi Limit 2 Fault may be associated with me turning the heater on & off too many times over a short period.) Water chemistry is good with the exception that Calcium Hardness spent 6 months in the 400 to 550 ppm range during the end of last year & beginning of this year, and the salt level is now at 4,400 ppm (3,400 ppm desired for IC-40). Any recommendations on what the issue might be (i.e. bad switch or partial blockage in water line) or how to troubleshoot it? Is there a detailed assembly/tech manual beyond the Installation & Operating Instructions Manual that would help in tearing down the heater to access the Water Switch?