The unit about 5 years old Polaris 380.., had the unit service, all parts working, hose ok, when cleaner is turn on lots of water comes out where the pressure relief valve connects to the wall outlet of the pool
you talking about the back up valve that backs the unit up when stuck or the actual relief valve that connects to the quick connect that goes into the wall? If you are talking about the valve that is by the quick connect fitting - that is supposed to discharge water when pressure is too high.
what RPM are you getting on your wheel?
If you hold it in the water and mark a wheel, count it as it turns while holding it in the water. should be between 28-32 I believe