The Pressure Differential Switch (Flow Switch) on my Vaillant Combi boiler (VCW T3W Sine 18) only works intermitently. I have a replacement part (VAIL 151017) Can anyone advise me on how to fit it.ie Do I need to drain the system?

Dennis McTaggart, January 2006

drain the water so that you don't flood your kitchen.
remove the bracket whic is usually pushed off, gently pull out the switch and then the copper tube.

What were the symptoms of your boiler. My diff switch does not engage and so i have no spark and no fire-up

Tony

Tony, September 2006