How to check for faulty water pump 04 2.8L Passat

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Much overheating -changed thermostat and o-ring seals in water and transmission lines going to radiator. Still have overheating! Having difficulty finding the rear coolant bleed valve near firewall on top of engine. Can you help with its precise location? Have bled the other two valves. Still over heating! Is there a simple test to perform to check if the water pump is faulty (plastic impeller broken)? Thank you We determined that the heater core is good by removing both inlet and outlet hoses and blowing thru the core. but no heat in passenger compartment. and after about 1/2 hour of engine running the temp gage wants to soar upwards towards the red-line. Appreciate any hel[p you can give us. Thank you