1.My Jandy pool heater was working fine on the low speed cycle of my 2 speed Jandy pump. I noticed yesterday the pool getting colder and discovered the pump not running on the low speed cycle. The digital message reads "No Flow". I know the bypass is off and all the flow is going through the heater. When the heater was installed late summer they had the bypass valve set to 1/4 open. In that position the heater would not function on low speed. With the bypass valve closed it worked fine. There is a round clear plexiglass cover over a red backflow preventer valve. (I think that's what it's for). That flap can be seen to be horizontal indicating a pretty good flow. The filter was just cleaned.
Is there a flow sensor that goes bad?
2. Does this heater, model listed in signature, have copper coils that will eventually deposit copper stains into my plaster later? If so, what do I do to prevent it?