Vailliant VCW242 hot water problem

[gvw]

Hi. This has a problem delivering hot water with heating off. It has a cam operated by a pushrod from the water valve. Observing the cam, it only moves about 2mm, not enough to make the dhw micro switch, and probably not enough to change the position of the servo valve. So the question is why? Is it likely to have a seized pushrod, or is the diaphram in the water valve? 25 years old, still works fine apart from this recent issue.

Thanks

 

[MrTherm]

The diaphragm is indeed the prime suspect, you will find the old diaphragm stretched/distorted. Stuffing box should be o.k but ideally should be replaced.
The two switch actuating spindles can be checked for free movement gap measurement while the assembly is removed, the gaps should be o.k if carefully left undisturbed.

 

[gvw]

Thanks for the reply. Have now checked the pushrod, it's free to move, maybe even a bit of a loose fit/worn, so the diaphragm is suspect. However, I have noticed that the dhw micro switch is missing the lower screw, and seems slightly too far away from the cam. Any thoughts about this?

Cheers

 

[Gasguru]

Pull out the water section and check the diaphragm first. Also check the Venturi tube is clean if fitted.
There should be a gap between the microswitch and cam at rest..the measurement is in the manual.

 

[gvw]

Thanks for the replies. I will order a new diaphragm and see how that goes.

 

[gvw]

While I am waiting for the diaphragm, I thought I would check the operation and adjustment of the pushrod. Now, I may be a bit dense, but I don't get these instructions in the manual. (See screenshot). The first part is fine, about adjusting the push rod gap by slackening the nut. It's the second bit about rotating the cam to provide a 5-7mm gap I don't get. If you rotate the cam it just gets pulled back by the spring! Is there something I'm missing??

 

[MrTherm]

1. With cam at rest (parking position) set push rod gap at 0.2"mm then fasten rod locknut.

2. Slacken screws (5) so that micro-switch is slightly loosened.

3. Now turn cam clockwise (per diagram) so that the 0.2mm gap that you have just set becomes wider to between 5-7mm gap (hold it in this position) then...

4. Gently turn the micro-switch body until the gap between the body and switch plate is about 0.4mm and secure the micro-switch in this, which will now be the activated position when ever the diaphragm lifts.

5. You can now re-check the operation of the spindle movement by pushing the spindle from below and confirm measurements.

Good luck

 

[gvw]

Thanks, that is much clearer than the manual. You should have written it!