It doe's not adjust but you should make sure it is in the right spot. It should be just after the first hose away from the wall at about 18". If it is in that spot it can't pull to far.
I'm not sure which pump fails after 15 minutes. Is it the main pump or the booster pump? The main pump works fine but when the booster pump is activated, one of them fails. What happens if you leave the main pump on and only activate the booster pump? Will the booster pump run indefinitely as well? They both share the same supply line. What have you checked so far? How old are both pumps?Do you pumps sound normal? Do the pump motors get abnormally hot? Any recent repairs or new symptoms? Is there a shut off valve on the supply line that has been turned/moved? Please write back with more information.
