That looks very similar to my Pondmaster pumps.

The diaphragms go out periodically and require a rebuild kit. That may or may not be your problem. They are not terribly hard to disassemble.

If the armature is stuck to one side by the magnet, the diaphragm has failed and let it pull to that side magnet. If it is still "running" but will not build pressure one of the diaphragms likely has a hole in it.

John

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