vaillant vcw 242 eh 1 tap not hot!

So I have the above boiler and it works fine.

I’ve always had to run the bathroom tap on hot to get the shower to go hot.

I’ve replaced the diaphragm in the water valve - the top was very rusty so I also replaced the stuffing box.

On putting it back together I could see the little rod was poking out more and I hoped that this would fix the issue as it wasn’t as prominent before - I was hopeful this would solve the issue as other taps trip the microswitch but the bathroom shower doesn’t!

It didn’t fix the issue - it’s like the rod isn’t pushing the rocker on to the microswitch enough - if I touch the rocker on to the micro switch the boiler fires into hot water mode when the shower is running but without touching it or opening another tap it’s not enough to fire the boiler.

Looking for any tips at all!

Thanks!!

Did you remove and clean the water governor and the guaze filter

Did you check the Venturi was spotless? It's the brass tube sticking out of the lower union in your last picture.
It helps to boost the low pressure applied to the topside of the diaphragm.
AFAIR it should unscrew.

All cleaned and spotless

Put it all back together and had a look today. turns out the pin on the vacuum servo that hits the rocker on to the microswitch has seized

Took that out and cleaned it and greased it and it’s working a treat now - although I think the ch thermo has now tripped as I’m only getting hot water and no ch now - aaaaaargh