Vaillant Comb - problems with hot water supply

[Nemo]

Hi

I hope someone can help me out here. I have a Vaillant Combi, it's either a VCW BG 242E, or 282E.

The CH side of the boiler works OK but the hot water (HW) is causing problems.

Most of the time when the hot water tap is turned on it gives cold water, but sometimes the boiler fires up and works OK. It does not appear to make any difference if the green switch on the front is in CH/HW or HW only - same problem.

There is also an occasional drip of water from the boiler, it appears to be coming from near the small white wheel/knob marked with red bands at the bottom of the boiler. Could some one please tell me what the wheel is for.

Also, the needle on the temp gauge at the front of the boiler (lower left-hand corner) is reading zero - not sure if the two problems are connected?

Cheers
Jim

 

[kevplumb]

check the pin is free under the servo valve

the knob is the water temp control

 

[namsag]

The drip you have is coming from what is known as the water section which contains a pin that moves up an down as the tap is turned on/off activating the gas valve. stuffing box on it is weeping and the pin will be scaled up and stickin(diaphram within is prob shot as well). If it`s been leaking a long time the grub screw that holds it in place will be rusted solid and may also need a new bearing plate, so depending on degree of damage parts will be from about £20 to about £150 if complete section and plate req.