I thought I'd update my progress in case anyone might be able to shed any
light onto our problems.

First thing I did today was obtain and fit a new DHW thermostat along with
the new NTC probe in the hope if I could get the boiler working the DHW
would stop overheating.
I vented the boiler and bled the rads -- no effect

I then removed the main control line from the servo to the diverter. It was
well clogged up with crud. I cleaned it out refitted and Bingo! Boiler fired
up first time and stayed lit. I could get CH or DHW on demand. The pushrod
was moving freely and tripping the microswitches as required. I ran the DHW
for some time and the water temp stayed constant and the pilot remained lit
so at least the water temp issue is fixed however the upstairs shower still
would not fire the boiler. (The BAth and basin were OK). In view of the crud
down the control line I decided to strip the others out and clean them too.
Hey, It couldn't do any harm could it?
How I wish I had taken a shower first.
The other Control lines were cruddy too and I took the servo off and cleaned
the holes the lines went into best I could - these too were rather clogged.
When I refitted and tried to run the boiler to my surprise and frustration
we were back to square 1.No DHW or CH.
The situation is as per my first post i.e the servo arm rises and falls at
the right times but the diverter pushrod is not moving at all. I can fire
the boiler by making the switches manually but it will only run for 30 secs
before cutting out - even if I continue to make the switch.
If I pull out the spring loaded microswitch trip mech away from the diverter
while the H tap is running I can see the pushrod begin to move out but as
soon as I release it forces the rod backin. There is not enough pressure in
the diverter valve to hold it though the tap is running full pelt.
Although I had the boiler up and running earlier ther was one thing that
caught my eye. On one occasion while calling for dhw the pushrod was
extending out smoothly to the right hand side when all of a sudden it fell
back then shot out again like there had been a sudden dip in the pressure.
I'm stumped now. I'm thinking of replacing the servo and or diverter valve.
Does anyone else think this would be a good idea?
What should I try changing first?
I'm taking the kids round to me mums for showers now!

"Son of Fred" wrote in message
...
I'm afraid the spindle/pushrod isn't moving the switches at all so I
can't adjust them.
I can fire the boiler by manually making the switches although it wont
remain lit.
The servo arm on top of the water section moves and returns OK.
I'm going to try venting the boiler this morning and if that fails
cleaning out the control lines this afternoon.

"geoff" wrote in message
...
In message , Son of Fred
writes
Our ancient Vaillant combi (VCW GB240H ) will no longer fire. The
culmination of a series of problems I found to difficult to diagnose with
certainty.


Have you checked the diverter valve microswitches ?


--
geoff