I've been driving around all winter in a hat and gloves, bemoaning the fact that my heater used to be good and now it basically didn't work at all.
I tried flushing the heater matrix out multiple times to no avail. I had resigned myself to taking it out in the spring and overhauling it for next winter. I also wondered if I was simply misremembering and the heater had actually always been like this.
The control cable hasn't been connected for a long time, since I dropped and lost the screw to secure it to the valve. I'd checked many times that the engine valve was in the position it would be with the cable pulled all the way out. "Pull heater" it says, right?
Fast forward to when I got back from work today in my freezing Traveller. I glanced down and saw "Push heater"! Opened the bonnet, changed the valve position and it instantly started working perfectly, nice and warm!
I've been putting up with being freezing driving it every day and all along it was switched off!

At least it's fixed now.

James