I just fixed this issue on my Scout. I used an endoscope to look at the flap motors (you might be able to squeeze around the pedals to see it, but it's just easier to use the tool) - for me, there were no issues, and they were moving around fine. The coolant in my expansion tank was a brown, muddy/scummy colour - not the lovely pink it should be. I then purchased: 1x New coolant tank without the silica bag - metalcaucho 03344 from Autodoc - you can use the old tank's lid 1x New heater matrix (double check part numbers before you buy, as there are a few different fitments) 1x 5L concentrate of G12evo (successor to the rubbish G13 coolant) 1x set of hose clamps (amtech 3 piece set) 5x 5L Distilled water 1x Bottle of coolant flush chemical Tools I already had, which you may need to buy if you don't have: Spanners, sockets, screwdrivers, big set of pliers, tin snips, torx bits, a 1 meter rubber hose with an internal diameter matching the outer diameter of the coolant return hose that feeds into the top of the expansion tank, a small victoria clamp to fit around the aforementioned hose, the garden hose connected to the tap (ideally with an adjustable and lockable sprayer on the end), a rubbish towel I don't mind ruining, plastic sheeting to go under the towel, a few buckets, and a tupperware container the wife hopefully won't notice going missing. I started by warming the engine up to operating temp, you can do this by driving around or just idling. Once at temperature, I disconnected the coolant return hose, put it into the rubber hose and secured the victoria clamp to prevent it from leaking - I then ran the rubber hose into a buckets, and let the engine run. The old coolant ran into the bucket, and I topped up the expansion tank with the garden hose, occasionally changing which bucket the hose emptied into so I could monitor the colour of the water coming out of the car. Be aware that if the water level in the expansion tank falls below the sensor, the car will sound an error on the dashboard. You don't have to worry about this as long as there's always liquid above the feed hole at the bottom of the tank. Once the worst of the discoloured water had stopped draining, I then reconnected the return hose to the tank and added the coolant flush - I let this run through for 20-30 mins. Whilst the coolant flush is doing its thing, it's a good time to prepare the heater matrix for replacement by removing the glovebox, footwell vent, centre console side panels and heater matrix retaining clip. BodriG has a good video on this, along with the rest of the heater matrix replacement steps: https://youtu.be/oHfQ_27dDRM?si=Rnah_XBRDNAvrNV5 Once the coolant flush had done its thing, I reconnected the return hose to the rubber drain hose and continued draining the coolant into a bucket and topping up the coolant tank with tap water. After the coolant had started to run clear again, I turned off the car and installed the new coolant tank and heater matrix. Once I had replaced both items, I then continued the flushing process, except this time topping up the tank with distilled water. I kept 1 bottle of distilled water to the side for mixing with the coolant, and once I'd used up the fourth bottle of distilled water, I then used the coolant concentrate to top up the tank - using 4 litres from the 5 litre bottle. Once I'd put 4 litres of coolant into the car, I reconnected the return hose to the coolant tank, reattached all hose fixings, and all was done! I also poured the remaining distilled water into the remaining coolant concentrate, such that I now have a bottle of readymix coolant to top the car up if required (I used a bit of this readymix to top the tank up to its correct level after I reconnected the hoses) Cleaned up all the mess I had made, and now my car's heating is lovely and toasty warm on both sides. There are videos on YouTube which run through the processes as well.