This broke on the drive home today (2000 Sprinter 208) and dumped all the water out of the system.
I bypassed it with an old sparkplug socket I had. This now means the heater core is always getting water circulating through it.
Does this matter? I live in a hot country so I never have the cabin heater on so it's not like I'm missing out on owt...
I doubt it's absent, but if you're not getting heat, then yah, maybe the core is blocked. My cousin was having trouble with heat on his Tundra, put in a new heater core and it was blocked off within days. We took it out and cut it apart and some goop had immediately closed off flow. Still mystified what reaction built the goop, maybe incompatible coolant types.