I have the same boiler and periodicaly have your problem too.
The solution for me and a great many others is to remove and clean/descale the dhw heat exchanger, its quite a common fault on those boilers.
Ive seen replacements if you dont want to do that from between 50 quid to 130 quid...
Hi all, did a bit of snooping 1st but I was unable to find an answer so here goes.
Ive a Vaillant 824e/828e which is about 10 years old now. Only previous problem with it is the famous hot/cold water issue to which ive cleaned out the dhw heat exchanger on a few occasions now.
Upto to day...