Vaillant VCW 242 no DHW or CH, diverter help

30 Oct 2006
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United Kingdom
I have a Vaillant VCW 242 running on mains gas; I have had a bit of an ongoing problem with it. The problem is that on request for CH the diverter valve does not move and therefore I have no CH, I have fitted a new servo valve, the DHW did work. Yesterday I fitted a new diverter valve and now the diverter valve does not move under its own operation at all, so now it does not give DHW or CH.

It is my thinking that upon request for CH or DHW after checks, a pressure is sent (via the servo) to one of the chambers in the diverter valve to either compress the spring and allow flow to the CH or to raise the micro switch plunger assembly and allow DHW. Does this sound correct? If this is case then has anyone got any thoughts on why the diverter is not functioning properly?

Pump working fine
Fan working fine
Ignition does work (in the case CH) if you depress the micro switch plunger assembly (request for CH is positive) and keep it depressed, the boiler fires and the radiators heat up and like wise if you demand DHW and pull the micro switch assembly out (so the second micro switch clicks) the DHW heats up.

I have also ensured there is no air in the diverter valve chambers and tried to bleed air as best I can from the servo valve.

Any help would be greatly appreciated
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Have you tried running it in heating mode and toggling the hot water on/off several times to force air from the boiler.

Did you replace the auto air vent? (disconnect pipe from pump to aav to access). It is essential that the water is free from air otherwise the hydraulic action on the diverter will be diminished.

Have you adjusted the water section pin so it correctly moves the cam on the servo valve. Have you adjusted the micro switches on the diverter.

Finally did you clean out the control tubes and flush them through. Also check the orifice is clear in the banjo connection.

Pumps on these boilers are bombproof and I've never come across one blocked/slow yet, problems are always due to above.

And read the FAQ's on expansion vessels. Valve is tight to get to (lower left side) and its normall to get a little water loss initially through the valve.
Wow, i checked the control lines and the one that goes from the top of the pump to the bottom servo was blocked :D

i have got to check things over as see if it all works ok but so far so good.

I doubt whether i now needed to buy a new servo and diverter but at least it is running

Many thanks for your help
My boiler has been working fine for 8 days but yesterday and this morning the heating has failed to come on. The thermostat in the house and switch are both demanding CH and the boiler has the fan and the pump running ready but the diverter has not fully retracted in to the position it needs to be to cause the boiler to fire.

My thought unless anyone has any others, is that due the blocked control line I had before there may be some silt in the bottom servo valve, do you think this might be the case?

Up until now we have had CH and DHW on demand.

Any ideas would be greatly accepted

Just to add that the DHW is working fine, if a bit slow to heat up some times.
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the main diverter valve should sit off the microswitches and the cam on the servo valve pushes up and makes the hw microswitch. Chances are the adjuster on the hw diaphragm spindle needs adjusting down slightly to let the servo cam drop slightly and allow ch to operate.
I’m still having a few problems with the CH, there does not seem to be enough hydraulic pressure to push the diverter value in and therefore give me CH. If you aid the diverter value in with a push and the micro switch makes contact then the CH comes on and stays on for a while, but the diverter valve slowly creeps back out again and I lose the CH.

The air is bleeding from the system just fine, all control lines are free, cleaned out any silt in servo and diverter is new.

What should the main system pressure be?

Can anyone explain to me the process for hydraulic pressure to push the diverter valve open? I can see it comes from either above the pump or below it.

The diverter is new and factory set so therefore should it need to be adjusted?

Its not the the microswitch plunger that needs to be adjusted as the main cam is not moving in on demand for CH
Is there anyway i could check to see if the pump is producing enough pressure to create the required hydraulic pressure in the diverter valve?

I can definitely hear the pump turning if i listen with a screw driver to the body of the pump.
Its not the the microswitch plunger that needs to be adjusted as the main cam is not moving in on demand for CH

No but it needs to be completely at rest, if there is still tension on the cam spring then your heating won't work.
When you say the spring completely at rest do you mean that the pin on the side of the diverter valve should be in fully so the spring is at its longest? if that makes sense?

Sorry for sounding an idiot but it is as if there is too much pressure building up on the DHW side of the diverter diaphram, forcing the pin/plunger out to where is should be if it was in DHW mode.

I understand there is a resting position (in the middle) out position (DHW) and in position (CH) on the diverter pin that sticks out of the end of the diverter. If i run DHW water the pin comes out and hot water comes on, if i put the CH on the pin does not move in at all (as it should upon request of CH). It actually creep out and no CH, which makes me think there is either too much pressure on the DHW side of the diverter diaphram or not enough on the CH side of the diaphram.

Any help would be greatly appeciated :D
does it sound like the servo valve is not changing over the flow to the other chamber in the diverter?

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