Vaillant VCW242 No Central Heating but DHW ok

[badtoad66]

First time posting on here but here it goes.

I have an ageing Vaillant VCW242 boiler that up until now has been working fine.

I have not had any work done on this boiler in the last 3 years since the heat exchanger was replaced apart from regular services.

The problem I am having is that the DHW side of the boiler is working just fine but when the CH is switching on there is nothing happening.

The pump, fan, burner do not start hence the diverter valve does not move to position for CH on. The flame lock out light remains off, water pressure is above 1bar and doesn't lose pressure.

I have tried with the pump in the constantly on position, using the bridge in the control box, which starts the pump and does move the DV into the correct position but nothing again not even the fan.

I have removed and tested the micro switches attached to the DV they check out ok, I have tested the CH over temp switch which checks out ok, I assume that the air pressure switch and fan are working ok as the DHW works fine, I have also checked the plunger on the Servo valve which is ok and clear of the cam, I have also bridged the thermostat/timer terminals to count out the timer.

Could anyone tell me if there is more I could try or if anyone knows what the fault could be.

Thanks in advance for any input you may have.

Tony

 

[AlanTownend]

Hi
Are there any external controls fitted & are they calling for heat?

 

[Bunnyman]

Put everything back as it was put the pump link wire into position 1, then remove all wires from terminals 3 and 4 . Put a link wire in 3 and 4, if boiler works then you have a faulty external clock or room stat, if it don't and sits there quiet with no pump or fan then it's a boiler electronic fault , post your reply back

 

[badtoad66]

Bunnyman, I have already tried what you are asking and suspected it could be one of the boards, the only problem is which board. Everything works as it should when the DHW is running so the fan and pump control would appear ok, its either the main board or the thermostat board (so I am told) what do you think?

 

[Agile]

Are you 100% sure the diverter valve switch is becoming open circuit when no DHW demand?

That would be the first thing an engineer would be checking!

Tony

 

[Bunnyman]

Pull the black knob off is spindle brass or white plastic ?

 

[badtoad66]

Agile,Yes the DHW diverter valve microswitch is open circuit when the DHW is off, the cam is in the correct position and when the microswitch is activated manually the DHW fires up.

Bunnyman, The thermostat shaft is plastic in answer to your question, why do you ask?

 

[Bunnyman]

Well because I'm a little bit of an expert lol, an I'm tryin to help you! There are 2 identical models of this vcw a hybrid and a non hybrid,you luckily have the hybrid as the non hybrids electrical system is totally different pcbs, if you look on the back of the mother board where the ch rocker switch is check for dry joints this is the common fault, if not its more likely the mother board that's faulty 130331

 

[badtoad66]

I appreciate your expert knowledge and have armed myself with the necessary kit to investigate, will let you know my findings.

Tony.

 

[badtoad66]

Bunnyman, have now taken the motherboard out inspected it and can find nothing that is immediately wrong so I guess I must now look to find a replacement, thanks for your input I will post with any further developments.