When it's boiling? Ouch, certainly a sign that the engine is hot.
If your first post - you said you replaced the water pump - it was missing a fin?
As in impeller damage?
Even a bigger OUCH - this is becoming serious!
If one of the pumps impeller fins separated, this can do even more serious damage as in now you have it grinding up and even plugging ports the coolant needs to flow thru,
So the bubbling - seems like it's not holding pressure - this may mean gasket issues too.
Ok, now this condition can occur when a water pump fails - but in the order of what you describe...
If the Radiator was changed BEFORE you discovered the impeller damage, then the replacement radiator may also be plugged to a point that the AC generates enough heat to overheat the motor because the CORE of the replacement radiator is plugged with sediment and impeller debris.
But when the impeller is damaged, no matter what - the engines first overheat from that condition may also be the sure sign the motor is failed - from the impeller damaging the block and the cooling jacket. The engine block - it's cast - so broken pieces and debris can damage the jacket to a point where it only holds coolant, and it can't circulate it effectively.
The grinding is a serious issue with any sort of debris or metal shavings - for they can ERODE the system, using the pumps impeller, to ABRADE and wear against the cast metal - reducing its ability to draw coolant, on top of, change in size of the ports it uses - can become enlarged to a point where the pump only swirls water - it can't pump it because the inlet and outlets are eroded to a point where there is no pressure build except for excessively high RPM to centrifuge the coolant into what's left of the system to even press out fluid to get to the radiator.
The Fiesta pump is similar but has only 2 ports; an Inlet, to the impeller - then the outlet to the jacket. The jacket is sealed within the cast block but has passages thru it to pass coolant around the cylinders to cool them. The flow is pretty brisk even at idle and most of the heat is pressed back into the motor - but also flows by and around the housing that contains the Thermostat and the Heater Hose OUTLET of hot coolant to the Heater core - the return hose arrives to the engine and is part of the INLET port.
So you have a two-fold failure in progress here from what I read, all the steps you've done aside from the second replacement radiator and a new flush to VERIFY the water pump in there - can pump fluid thru the system. You have to make sure the pump is pushing coolant into and thru the motor, and it is sound enough to continue working - for when you're at idle - the issue of those enlarged ports and debris shows up as bubbling and that means; no coolant - or not enough coolant - is moving thru the system at idle speeds - boiling the coolant because it can't pull enough heat out of the engine to the radiator.
I can only hope I'm not right...
