Vaillant VCW 221H Servo

[Slugbabydotcom]

I have been looking at a vaillant VCW 221H
When in heating and hot water mode after running a tap I found that pushing down the right hand side of the servo cam caused normal operation.
It is as if the spring isnt strong enough.
I believe have ruled out a problem with the water section by pushing down only on the pin. This had no effect.
I adjusted the microswitch to its maximum to give more clearance but this had no effect. The microswitch does not break the circuit until the cam is pushed down manually.
I intend to go back tomorrow and renew the servo as I am fairly sure that this is at fault, however from previous experience with these older Vaillants I know that this could only be a symptom of a problem and not a cause.
I know to check the tubes for blockages but apart from this does anyone have any advice or pointers on what to look out for? Maybe a pump not providing enough vacuum or pressure to return the cam to its correct position?
I know my way around other boilers quite well but Vaillants always were my bogeyman and I usually manage to avoid them

 

[kevplumb]

pins have been known to stick if the gland leaks slightly try stripping cleaning and grease the pin

 

[weargas]

operate the lever of the servo manually (without opening a hot tap) when you let go see if it returns to normal and operates the microswiches on the diverter valve. If it doesn't then renew the servo, if it does then the servo's alright and the problem is with the pin and stuffing box on the water section or the pin between the servo and water section. It's a test so simple you could teach a monkey to do it. The hardest part is finding a monkey (and getting kev not to hang it)

 

[Slugbabydotcom]

It didn't so I'll try the servo and report back.
About the monkey tho. My daughters b/f is from a place where they hang the odd monkey and I'm convinced he has prehensile toes. So my theory is that the Monkey got into the gene pool before they hung it.
My dilemma now is:- Is it worth fighting my way out of the smog for the services of someone who is at best only 1/128th monkey?

 

[gasman24]

It will almost definatley be the pin scaled/siezed on the water valve have changed loads of these on vaillant vcw`s

 

[Slugbabydotcom]

I've sorted it out now.
Inside the water section there is another spring loaded pin that comes up from the flow restriction device. This pin is held in the correct position by a brass 'bridge / washer' which had de-zincified and snapped.
This prevented the diaphragm assembly from returning to its proper position.
I replaced the water section completely and everything is working fine now.
Many thanks to all who have posted replies and goodwill to all monkeys everywhere