How can I fix my Vokera 20/80 RS Flowmatic?

The venturi does not need to be 'blocked' not to work, it only takes a little bit of dirt or corrosion. However your fault doesn't sound much like that. Dirty venturi cause the hot water to run hot-cold-hot. If the problem is for both hot water and CH not firing up on demand I would guess the flow micro switch is either broken or not being actuated. A corgi man should sort it.

c
May 2009

Check Air pressure switch does not chang over

Mr K
May 2009