[QUOTE=LMG5K;590890]Ok, so ive wasted about 1litre of my 2 litre bottle of patio cleaner!
After testing with a hose, my matrix does have some flow, but not a lot.
My Matrix was so completely blocked a pressure air line pressure washer etc failed to get any flow at all !
I was worried not to damage it & did not fancy the acid answer to unblocking, so afer months of cold car tonight I vibrated the blockage loose instead .
Now don't get the wrong idea, I used an adjustable vibrating neck massager similar to this link, but older with a flat disc, but the same principle.
Other appliances may work too, but I had none to hand (honest)
The massager I had has an adjustable frequency, so I got a large clear plastic jug and with some particles in the water I ran through the frequencies until I found a harmonic (or resonant frequency) that made the water ripple and the particles to jump around the most.
With that frequency setting, and the engine running hot, and with the glove box out I was able to apply the 'massager' to the pipes and lower plastic matrix housing (with foam cover removed) and after a while I got a little heat, which indicated a limited flow.
I switched off the engine, and carefully removed the hoses (I'm an expert with that clip now) and put a Washing machine hose on one pipe (the large rubber end) and directed the flushing water away from the engine, and I jammed a garden hose (with tapered nozzle end) to the other pipe end.
The flow was slow at first , but gradually the flow increased, and after a while I swapped the Hoses over and pushed water back through in the opposite way until it ran clear.
I then topped up the anti freeze / coolant and restarted the engine. I now have a 'fairly warm' heater, but I think from reading posts above that I will just need to do a bit of bleeding to get it up to full heat(and possibly a few more flushes will do the job)
Worth a go if your matrix is really blocked with no flow at all.