mk2 golf heater problem

No heat at all coming from heater, I've changed the core, flushed the system, checked the hoses. The heater flaps are deteriorating but not dramatically. Still cold air only, I've just wasted a whole day trying to sort this and nothing, I've also tried shouting at the cat and banging my head on the steering wheel. Nothing. Please help.

I'd scrape all the foam padding off the flaps inside the air box & cover the metal perforated flap doors with foil furnace tape.