I originally had a above ground pump that was pumping about 9 GPM into my 5 ton system. Now I have a submersible pump that is pumping 14GPM. Problem is the pump turns on for 5 seconds and shuts off. a minute or later does the same thing. Pump is hooked directly to the system as was the other one, when calling for heat, the old pump would turn on and run till there was no more need for heat or cooling. Is a bladder tank nescessary?