After replacing the water pump the heater stopped working

Hi,

Chances are there is an air pocket preventing the coolant from flowing through the heater core. Try this. Start the engine, turn the heat on high, fan speed on low, and allow the engine to reach operating temperature. Make sure the coolant level remains full.

Next, feel both heater core hoses under the hood, both should be hot. I suspect in this case, one will, and one won't be nearly as hot. If that is the case, allow the engine to cool. Loosen the clamp on the cooler hose and start the engine to allow any trapped air to escape.

Try that. Also, let me know what engine is in the vehicle and how the system was bled.

Let me know what you find. Also, here is a link you may find helpful:

https://www.2carpros.com/articles/car-heater-not-working

Take care,

Joe