I know I don’t need it at the moment but I want to sort it before the cold weather arrives. The heater in the van takes a minimum of half an hour to warm up, and then it only gets mildly warm, never toasty even on full blast. The fan is fine, so is there a problem which could be sorted by flushing the heater matrix out somehow? Cheers.

Common thing on VW engines is an air lock on the heater matrix pipes meaning they dont have sufficiaent coolant in them. Find where the two big bore pipes enter through the bulkhead, with the expansion tank lid removed start the engine with the heater set to full temperature. Squeeze the pipes with as much of your hand as you can get round them to force the air lock free making sure of course that you top the header tank up as the coolant level drops. It may take five or so minutes before you have forced all the air out and if that fails you can make an elevated header tank to put it above the level of those two pipes and fit it to the expansion tank and use gravity pressure to move the air lock but its a lot more of a faff than just pipe squeezing the pipes.

Could also be a dodgy thermostat allowing coolant to recirculate without ever fully heating up.

Thermostat housing common failure, but it usually means it gets too hot, but might be worth a check. They are plastic, and with time, the piece that takes the pin from the thermostat pushes through.

Normally if stat or sensors in that area are u/s it will throw up management light and go onto fallback ie cut out turbo in my experience but go with the pipe squeeze first, its the normal cause.

Thanks guys. Will give the pipes a good ole squeeze and see what happens?

I had similar on my Sharan and it was the thermostat.