CLR Flush

I was shocked when I saw the condition it was in.
Question.....Before I pulled it apart, I wasn't getting any heat. I assumed my heater core was blocked. After the flush and a new thermostat, I'm getting heat. I assume it failed in the open position. Would this have restricted flow to the radiator?

Failing in the open position should have made the heater flow and have heat unless the engine was not warming up enough because of it failing open.
That would explain it.