How to change the heater matrix. Took less than hour. Heating restored. I should have just clapped off the heater hoses at the bulkhead and probably it would have bled the air out when I unclamped them and topped it up, but the factory vacuum fill the cars and that eliminates air pockets, when you just pour water in the bottle it doesn’t always displace the air and sometimes the heater will still be cold or it may suddenly burp itself sometime later. But it’s an easy job and a good earner.