Low pressure on a Hayward DE Filter

[mas985]

Assuming the normal filter pressure is higher than 4 PSI, it is likely that you have either a clogged impeller or a clogged suction line. The impeller inlet can be check by removing the pump basket. If that is clear you can try to back flush the suction line.

[vinper]

what happens if you close off the return valve to pool ,what does pressure go up to?