When I turn on the cold water taps everything is fine until I turn the tap OFF. Then the pump (not the burner) on my Vaillant ecoTEC 828 starts and goes off after about 15 secs. If I flush the loo or use the cold water basin tap this does not occur - only applies to cold water taps in kitchen and on the bath. What could cause this ? The boiler has just beeen resited.

Tim Goadby, November 2011

Carefree - thank you very much indeed for your reply -its much appreciated and what you say makes perfect sense. I'm sure this will enable me to solve the problem.

Tim Goadby, November 2011

Most likely, a 'dead leg' in the hot/cold water system (a length of pipe running to a dead end), this will cause the aqua sensor to spin as the dead leg re-pressurizes after use thereby bring the pump in to life.
Find and cut off the dead leg, or alternatively, fit a non-return valve on the cold water inlet to the boiler.

Carefree, November 2011