water pump on 2002 Nissan Altima

My heater only get hot if I'm driving over 40mph,,took it to dealer,,they said the hose needed bleeding or bubble in the hose something lik that,,,got it fixed heater worked maybe 2 months,,,took it back now they say its the water pump making the heater not work, how do you check water level for the pump? Cos I never see water leaking from my car,,I think they are taking advantage of me,,,,thanks for your help

Asked by for the 2002 Nissan Altima
water pumps don't always leak when they are bad. The water is pumped around your engine and through your heater core, By the water pump. It has fan type blades (impellor)
that will rust off if your running mostly water in your radiator. Or if it is the type that is made of plastic, the blades might have broken. Also known to come loose from the shaft, and just free spin. Any of these problems will cause you not to get heat as needed and not leak water.
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You cannot check water level for the pump, the water passes through. Sounds to me that you need a second opinion. Can you bring it in?