I have a Hayward variable speed pump that is a little sensitive in that it will not get past auto prime (15 minutes) from time to time. This is typically my sign that it is time to backwash. Recently it will not prime when my valves are turned to hot tub but works fine when turned for pool flow. There was air coming out the port when it wouldn't prime. I let it prime for the pool, then turned the valves to hot tub and all was well. No air coming out of the port until I turned on the jets.
Two questions - how bad is it for the valves to change the flow when the pump is running? Second, any thoughts on where the air was coming from? There is no leak, otherwise there would have been air in both cases.