Q: why is my van heater not working

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i put a new thermastat but my van wen its on my heater gets cold then we i accelerate it it gets back to hot,also wen am driving my temp needle stays on cold but wen i stop it goes up

My car has 150000 miles.
My car has an automatic transmission.

There are several issues that can be the cause of this. The most likely is, unfortunately, the heater core. You may have to replace the entire unit if that is the case. With that said, you should always start with the simple tests first. Was the heater working before you changed the thermostat? If so, the new thermostat may have been installed incorrectly or was a faulty unit to begin with. Air that is trapped in the cooling system can cause similar symptoms. This will require any air to be bled from the highest point on the system. If the overflow system is working correctly, over time the air will work its way out on its own. If you need assistance, a certified YourMechanic technician can help inspect your vehicle’s heating system and diagnose this issue for you.

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