Vaillant VCW-GB-242-EH Electrical Fault

Hi Folks, new to this great forum...

Put the heating on last night and found the rads stayed cold. Investigated to find the boiler not responding to commands from timer or 'summer winter' switch. The system tries to fire the boiler (which immediately shuts off) and the pump runs continuous. This situation remains even with only live and neutral supplied and no switch connections. Hot water works OK though... Can I assume the controller is knackered?. As it stands at the moment, I have to power down the boiler until i need hot water when I'll switch it on until I have finished using it.

Hope someone can help with this one. Thanks.

This is an old model, quite complex in the number of components, but not unfixable. As long as you dont disturb the inner combustion chamber cover, or touch the gas supply I have the following tips:-

1. With the outer cover off there is a stainless steel disc arrangement at the bottom of the boiler (bottom centre-front) which is the water section & has 4 pipes connected to it. Has the pin in the centre stuck up?

2. The pin acts on a cam which operates a microswitch and a servo. Has this stuck up?

3. The cam also diverts water to the diverter valve at the bottom right of the boiler, easier to get at with the side cover off (one or two large screws to loosen only.

3a. If the pump is running and there's a min. of 0.5 bar in there, the pump provides the thrust to move the diverter valve right or left.

So my first check would be to check the system pressure, then that the water section pin isn't stuck up or the servo hasn't stuck.

Post back so we can see if that's successful; ego stroking lubricates the typewriter keys!

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If the hot water switch is not correctly adjusted (ie insufficient clearance) the servo cam can jam (and stick) against the switch lever as it rotates round setting the boiler in permanent hot water mode.

Oh good grief!...... yep the rotary cam had stuck, should've looked there first as i had a HW issue a few years back had to change diaphragm and adjust this switch!. Well Thank you so much for such a prompt reply and subsequent quick fix.