Finally got around to flushing out the heater matrix on my old 2011 diesel right-hand drive. Pleased to report the cabin heater now works, just in time for winter.
First open the drain cock on the radiator and let the coolant drain into a bowl. When it's stopped dripping, put the drain cock back in and remember to tighten it up. Remove the air filter cover and the big hose which goes to the turbo, with a smaller hose that branches off to the rocker cover vent. This hose may have a bit of oil in it so be prepared to catch the drips. Cover the open mouth of the turbo with a plastic bag to stop any debris or water getting in it. It's not easy getting pliers onto the hose clips, but loosen them off and slide them along the hose. Use a flat blade screwdriver to lever the hose off the heater pipes poking out of the firewall, once you get a bit of movement to break the seal the pipes pull off pretty easy. Good idea to put a bit of tape round one of the pipes so you know which stub it came off.
I bought a metre of 19mm clear plastic tube from B&Q, it's a perfect fit to go over the stubs. I cut about 150mm off, then slid a piece of plastic electrical conduit through it, then pushed my garden hose through the conduit. That was a bit loose but only let a dribble of water leak out. The rest of the tube went over the inlet stub and routed downwards so the water spilled out on the ground. Turned the hose on for about 10 sec to flush out the matrix, then turned it on and off a few times for a couple of seconds. Then swapped the hoses over and did the same thing, with the flow reversed. Finally, swapped the hoses back again and gave it a few more squirts.
Re-connected the heater hoses, put the air filter and turbo hose back on, put the air filter back on, then re-filled the coolant tank with what was drained out of the radiator. Not all the coolant would go in at first, I had to drive the car around for a few miles to make sure the engine was up to temperature and the thermostat had opened, so any air pockets could find their way out. After that, the coolant level had dropped so I could get the remaining litre or so into the header tank.
