Hello, my friend from NC recommended I visit this site since it helped him tremendously. I've read all the chemistry topics and general guidance so I feel at least a little comfortable with the basics. Where things get all wonky is with a strange situation I've run into with my spa/pool heater. Our Jandy system is set up with pool mode and spa mode which basically controls the input to the filter and the output back to the pool or spa. When we fire up the (brand new) RayPak 406A (400btuh) in the spa loop (spa drain in > spa out) the heater fires right up and it works great! But when I put the system in pool mode (main drain in > pool out) the heater says it doesn't have enough pressure to fire. The odd thing is that there is plenty of flow and I have a good prime on my 2hp pump. I've tried everything, completely cleaned out the filter (I get 25psi by the way when it's in the pool loop), I've tried swapping inputs, I've even tried running it with the pool cleaner booster pump running and no avail. I have also tried running it in the spa loop, and swapped the output valve from spa to pool and the second it gets half way there the heater shuts down throwing the pressure code.
Does anyone have any idea why I can't get sufficient pressure when I'm in the pool loop but I can when I'm in spa?
Diagram attached for reference...