Powertrain / Under The Hood • Sudden loss of cabin heat at idle

2015 Flex Limited (Ecoboost) / 140,000 miles

-Coolant was last flushed and replaced 2012 / 80,000 miles
-temperature reads 'normal' on the dash
-coolant level in expansion tank is good and has not changed / moved
-no coolant traces on the ground
-no coolant smell in cabin or exhaust

This just started happening today. It's in the 20's here in the Milwaukee area. When the engine is at operating temperature, there is basically no heat blowing inside the cabin when the car is in park and idle.

As soon as the vehicle is being driven, normal heat returns almost immediately. While stationary and in park, some heat will blow if I raise the engine RPM's. If i turn off the engine, let it 'rest' for about a minute then restart, some heat will blow (parked at idle) for a moment, but then become cold.

Blend doors all seem to operate correctly. I don't believe they are part of the problem, but?

Later tonight, when I'm home and the car is fully cool, I will check fluid level at the radiator [cap].

Anyone else experience this? Any suggestions?

thank you in advance-
Eric

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