Well, finally managed to get the dryer part working again - though possibly helped by the fact I still have a couple of years of a 10-year warranty to go.
(I've posted the history leading up to getting this repair elsewhere in this forum -
First of all, I have to say that the Miele warranty repair admin seemed OK - in other words when I phoned them I got through pretty quickly, they found my warranty details and then made an appointment about 10 days away, then did text me the day before as a reminder. So, that part works.
The phone was answered by a nice enough young kid - but he was clearly trained in how to push blame for any washer-dryer failure promptly back to the customer:
After explaining symptoms (no fault code, but no hot air for dry/steam, horrible white gunge being put onto washing in drum during every other wash) he asked me "and are you aware of the Rinse Out Fluff feature?" Could have been my imagination, but the way it tripped off his tongue meant that he was well used to asking that question and getting a confused 'No?' from the owner (after all, the RoF feature is only mentioned in the middle of the lengthy manual, which probably half the customer base will never bother to read).
"Yes", I said tartly, knowing what was going to be coming next.
"Right... and have you remembered to use it AFTER EVERY DRYING CYCLE?!" - Again, the rising tone in his voice suggested that many of the poor s*ds who answered "Yes" to the first question might have made the mistake of answering "No" to this second question.
I could have wasted a bit of time by reminding him that the language in the Manual regarding the RoF feature was not exactly apocalyptic: "Run the Rinse out fluff
programme before the machine is used again so that fluff cannot be deposited on the next load (e.g. fluff from dark garments being deposited on lighter coloured items) or cause a blockage." And this just located on p.45 in the manual.
(As we now know, for many Miele Washer/Dryer owners, the RoF feature should really be in red ink, with words along the lines of "Please remember that if you don't use the RoF function immediately after every single use of the drying function, your £2000 machine is likely to break down just after the 2-year warranty expires and cost you upwards of £500 to repair. Your call")
After all the hours wasted researching this fault, I decided to be polite but firm "Yes, every time. And I am well aware that this issue is due to a design fault common in Miele Washer-Driers, whereby soap powder congeals along the hot air system and cannot be cleaned out by the end-user, thus leading to issues with the safety thermostat and other parts."
What was interesting was that as soon I said this, he did not faff around going off to 'ask his supervisor' or similar, but immediately booked the call. It is possible that he and other customer-facing colleagues know the issue with the washer-dryers, and so when confronted with someone who clearly knows it too, they give up trying to blind customers with science.
Anyhow, the repair guy duly arrived and fortunately he was not a dud. He was excellent, very efficient, actually able to work on the machine at the same time as discussing it, and very loyal to the company (probably too loyal - he avoided giving too much away about these dryer issues when asked direct questions).
I had been ready for an engineer who simply walked in, reset the thermostat and walked out - but as soon as he stepped through the door he said 'This will take about 2 hours', so I knew that either he was going to do a full dryer system clean out or parts replacement. Turned out to be the latter, i.e. he brought a top element box and fan, and a long plastic oblong duct thing, which I believe connects the heater to the suds container below?
Pleased to say that when he took the various panels off, the machine itself inside looked very clean - which of course it should do after we have religiously bought and used all the various over-priced Miele de-lousers, and given the fact that it has probably only had the equivalent of 3-4 years use, if that.
The key question - how the supposedly intelligent electronics could not detect that the heater was no longer heating and display an error code - was one he couldn't answer, or maybe preferred not to (I assume the real answer is along the lines of "yeah, I know people pay £2k for these machines, but the design guys don't think it worth putting in another temperature sensor that would pick up on the fact that no hot air is coming out during a drying cycle ..."
As someone who generally respects German design, I was still intrigued as to whether this dryer failure issue was just a design flaw in my machine series and older, so asked if the drying system was the same in the new means. "Yes, fortunately!" he answered enthusiastically.
This did perplex me a little - I can only assume that most repair guys take the view "sure, the system our machines use gets gunged up and conks even if you do use the RoF feature, but at the end of the day all we need to do is replace these two parts and it is rendered as good as new - and of course Miele customers can afford to pay, otherwise they would not be buying machines that are 2-3 times the price of the competition"
A warning to anyone just about to purchase a new Miele washer/dryer I guess.
Some might say that I am being a little harsh, but I know exactly how well cared for this machine has been, and how we have always used the RoF feature after every dry - so heaven help a harassed mum/dad with 4 kids and 12 wash/dries a week and no time to read the manual or use all the various Miele machine cleaning products.
I'd have more respect for Miele if they took two simple steps - #1, move the Rinse Out Fluff instruction to page 1 of the manual or maybe #2 simply build a Rinse Out Fluff cycle into every drying cycle (you open the door, take the dried clothes out, slam the door, it RoFs and then turns off). While we are at it, maybe #3 - spend a Euro or two on putting another over-heat sensor near the heating element that gets gunged up, so that at least the machine gives a reliable error code - I never got the infamous '55' error displayed, which for all I know meant that the fan stopped working but the element was left getting hotter than a nuclear reaction inside my white box.
BTW, out of interest, I downloaded the Manual for their newest, priciest washer-dryer, to see if it had been updated in anway - nope, same wishy-washy text re Rinse Out Fluff, buried deep in the centre.
Fingers crossed that when ours goes again, it is in the week before the expiry of the warranty...
Thanks to the various people here who contributed info that enabled me to talk knowledgeably to Service Centre and so secure a decent repair first time around.
For google: Miele washer dryer WT2780 WT 2780 drying problems issues cold air no 55 error message debris gunge white grey on clothes Waschtrockner lave-linge sechant