So basically the heat does not work unless you are moving? If that is the case then we need to do a couple things first.
It sounds like the only time the heater core is getting the hot coolant is when the RPM is raised which will push the coolant through the system.
Let's start with a pressure test and make sure there are no leaks.
https://www.2carpros.com/articles/radiator-pressure-test
It should hold pressure for at least a few hours.
If it holds pressure then you need to make sure it is topped off. Once you fill the coolant, retest the heat and see if it is better.
Let us know what happens with this. Thanks
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Wednesday, November 25th, 2020 AT 1:47 PM