Vaillant VCW 242 DHW problem

[yossarian83]

I have an ancient Vaillant 242 which has worked faultlessly for nearly 15 years. I’ve had it serviced annually, and it’s just gone on and on. However, the guy who’s kept it up for me has recently shut up shop, just at the time when it’s developed a fault. Noone locally wants to touch it, saying it's not worth the time and effort.

Changing it is not an option - I just can't afford it at the moment.

The DHW is intermittent, sometimes it comes on fine, other times not at all. I have a service manual, and have confirmed that the servo value is throwing over correctly, and that the plunger on the Diverter Valve moves left closing both micro switches. However, sometimes the CH flow pipe gets hot, indicating the valve is letting-by.

What I don’t understand is how can this be an intermittent fault? Before I strip and overhaul the DV, could someone confirm that this is likely the cause?

For info, the DHW H/E is the later plate type, although I’m not sure if the DV diaphragm was changed at the same time.

Thanks in advance for your help with this

Chris

 

[aaronH]

The variation of hot water performance could be explained by variation in water pressure. In the centre at the bottom is a silver hot water section which shouldf have a grey knob on the front for adjustment. On top of the section a pin moves up and down and moves the rocker to hit the microswitch just behind the servo.

When the water pressure is low, when a lot of other people are using their water the pin may not rise enough to activate the microswitch. When the water pressure is better it will work fine. It may be that the water section needs replacement, this may be because the diaphragm has stretched inside. Alternatively, there may be a slight leak under the pin causing stiction and needin water section replacement . The height of the pin could be adjusted, but getting the spring that returns the rocker back on can be a nightmare.

If I remember rightly, when the heating is on the diverter on the right should be fully in, hitting both microswitches. When it goes off and the pump runs on it should move out to release one microswitch, and when the hot water runs it moves right to release both microswitches. Better check on that though

AH

 

[DP]

Great boiler not many are able to fix.

Ask here who DOES understand and CAN repair this boiler. Get him to fix this boiler. Earlier Vaillant T3 model at 25 years is still giving faithful service to many. At 15, VCW is still a pup.

 

[aaronH]

When you say the DHW HE is of the latter type, assume the original was a black plastic looking one that has been replaced with a smaller stainless version.

It could be that this is crudded up with crud in the system, or scaled up.

Check the movement of the pin/rocker next time the DHW stops working, can you push it over to the left to close the microswitch and fire the boiler, or is already fully closed?

AH

 

[yossarian83]

OK, thanks for this. I've now got things to look at next time it's on the blink.

The H/E is indeed the smaller stainless one, and I'm fairly sure it's not clogged - when the thing is working I get about 35 degrees rise at 9l per min - a little down on spec.

I will look into the suggestion about pressure - I know the water section was replaced within the last 3-4 years. Unusually for this model I can adjust both the flow rate and the temp control - everything appears free and moves as expected.

It's a little tough to diagnose the problem as you can usually clear the fault by turning the tap on and off a couple of times, and by the time I've got the front panel off things always seem to have resolved themselves !!

I know something is definitely wrong though as I can feel heat in the CH flow even when the boiler is switched to DHW only mode. Surely this shouldn't be the case.

I'll keep poking around and see if I can provoke the fault reliably.

Thanks for your help to date - I'll post again when I've got more info.

Chris