F.37 (837/637 Models Only)
Quote: "The rotary speed of the fan is too high or too low"
Answer: The Air Pressure Switches on earlier models are a pain in the neck and often suffer with this issue, exchange the APS and you should be good to go again.
Vaillant part number: 05-0577
GC part number: E49-977
Best of luck.
BTW; the APS can be found behind the boiler on the top-right... It's a bit of a struggle to change, especially if the appliance is installed close to a ceiling.
ccMods
July 2006