Vaillant Turbomax VCW 242E

We almost need a FAQ for VCW 242's! Frankly this is a £250 quid job which ever way you add it up. The job does not scare me but it is definitely not for beginners. The manual which is absolutely essential is available from Vaillant. Any pro who takes this one with out allowing for a solid 1/2 days work is either inexperienced, naive, a genius or a fool or a combination of those. This boiler is 10-20 years old, it's by no means at the end of it's life yet but this is likely to be a non-trivial repair. Expect problems with washers, limescale and corrosion.

You can download manuals from

Yep, in Dutch.

This one might be a fault my 242 suffered from, and appears a common one. As far as I remember, its not usually the diverter at fault, more the DHW flow sense microswitch.

As I understand it, when HW is demanded, a flow switch detects this by a diaphragm moving a small plunger until it contacts the HW microswitch.

On a badly affected 242, the plunger moves oh so slowly towards the microswitch, taking 30 seconds or more if at all.

You can see it in action if you take the front panel off, there will be a central shiny piece of 3/4" (?)tube with allsorts attched, and a red microswitch positioned close above or to the side of a mechanism attached to the tube. If the plunger works at all, you'll be able to see it in action, even if slowly.

The cause is corrosion I believe. So, it may be the DHW sensor/diaphragm/plunger mechanism that is stuffed, not the diverter. Sorry I can't come up with a less rambling explanation.

Ed Sirrett knows, and has commented on this before.

Andy.