1984 Westfalia 1.9l A/T

Vanguards,

A bit of help, please.

Since replacing the steel coolant pipes beneath in August, I can't ged rid of the blinking red light. (Silver lining is I did discover broken sway bar link - now fixed)

It began halfway into a 12-mile drive, but now blinks constantly. 

So, I thought, I'll evacuate an air pocket, and all will be fine. Thus far I've followed Bentley instructions, the raised rear-end bong, and front-end siphon and refill. I disconnected the two radiator hoses and did multiple clean water flush and drains. The radiator seems to flow as it should.

What incredibly obvious solution am I overlooking?

tia

Kevin