You have 3x coolant pumps!
The main belt driven pump (electro-mechanical - with an electrically actuated shroud to
help speed up engine warm up), and 2x electric pumps.
The Charge pressure pump from your fault code is one of these small electric pumps.
This is on a separate low temperature circuit down behind the radiator (just 'topped up' by the main circuit) - compared to the main pump and the EGR/heater matrix micro circuit.
If you can hear gurgling, that is air in the system, but is it an air lock which was there since the heater matrix change - or from recently loosing some coolant?
That will be why you aren't getting good heat into the cabin.
Have you lost the coolant again since topping up last time?
Were the rear hoses behind the engine disturbed during the heater matrix change? As those were leaking as in the first video I shared.