Ya, op got it figured out thx to you that’s the important part. I just wanted to add a little clarity for the poor bastard that will come across this post after googling “Ford Focus coolant leak”.

I’ve only seen bypass valves that block off one of the two heater core hoses to prevent flow but not both. Same idea as a thermostat blocks only one side of your radiator to prevent flow. So even though coolant isn’t flowing, it is heating up and pressurizing. There may be vehicles out there with an unusual design that blocks both inlet and outlet hoses to the heater core. But this isnt one of them.

Not trying to argue, just trying to share some of my knowledge as a former Ford tech.

Even with that design it would leak coolant. The bypass just prevents the flow of coolant but it should always be primed with coolant even when it isn’t flowing.