upper hose be still when running as water is being pumped through. squeeze in hand should bounce right back and thinning of walls with older hoses can be seen with inspections. lower hose should also have a spring in it to help in the anti-collapsing . sounds like you may have a weak pump, and if its new to you, as you haven't did this already, then id would just plan to replace pump just for good measure. not to say drive it a bit and see if it wasnt just that cap and some air. water is flowing either way. but does it maintain temp...