Sambucus, part of the elder family?

I have had this bush/tree for approx. 15 years and it is about 10/11 feet tall.
Problem is main branch looks to be dying, leaves all droopy whereas an offshoot starting from near ground level is healthy.
Local garden centre cannot see any disease only a few aphids and are at a loss as to the reason.
Should I cut it back and if so is this the right time to do it