I've read some previous threads concerning this topic but still can't get my problem fixed. I have a Doheny's 1.5 hp pump hooked up to a hayward sand filter. When the multiport valve is set to filter the return pressure is very low, but if it is switched over to recirculate then the pressure is fine. I have tried backwashing the filter and priming the pump again, but all was to no avail. Has anybody else had this experience.