Vaillant VCW 20/1 T3W - Help and advice Required?

[0308marshman]

Hello friends,



I hope that you can give me some advice. I have a virtually unused Vaillant VCW 20/1 T3W Serial Number 20465347 installed in a chalet in Lydiate, Merseyside. Everything has been turned off for some time. I have cleaned the boiler, turned the propane back on, have the water flowing through it and the pilot light lit, but nothing happens when I turn the tap or the heating on. Is there a procedure that I can go through to start the boiler, or to eliminate or identify faults? Any help or advice very much appreciated as I cannot find any literature on this model.



Kind regards,



Eddie Marshman.

 

[namsag]

IF its been laying idle there is a good chance pump has stuck take the big silver screw out the middle and spin the shaft with a small flat bladed driver even a couple a gentle taps with a hammer to the pump with one hand supporting pump should free it

 

[0308marshman]

Many thanks for your suggestion, I have just checked the pump as you advised and it is turning freely.

 

[Agile]

Presumably you mean the pump turns freely but the boiler is still not working.

But you dont say if the pump is turning on its own when you try to use the boiler.

Its usual to have boilers serviced every year. Its possible there is a simple problem but there are not many engineers left who are very familiar with this model as they are now about 20 years old.

Tony

 

[namsag]

There is a little black rubber overheat button on the (i think) righthand side that may need restting,.

Also these have an unusual pilot mechanism and although pilot is light it has not engaged properly , push the off button firmly to turn pilot off and relight it and see if that helps

 

[0308marshman]

Hi,

many thanks for your reply, the pump does turn freely and does rotate when I try to start the boiler. The pilot light is lit but the burners do not fire up at all. Can you think of anything that I could check to to see why the gas is not getting through to the burners?

Kind regards

Eddie

 

[Agile]

In the middle there is a black plastic ( or shiny metal ) lump with two thin tubes going off towards the pump.

This is an interlock on the gas valve. Behind it is a pin which moves when the pump starts to enable the gas valve to turn on. This may not be operating.

If its not the o/h stat as previously mentioned then there may be air in the system and that pin may not be moving.

Tony

 

[DP]

Operate the right hand switch. Does the burner fire? Has already been said- check O/H cutout is in reset position.

Regret this boiler is a little complex to give guidance from afar. If you have a manual, look at the flowchart. It might help.

 

[0308marshman]

Many thanks to everybody for all of your suggestions, I have tried all of them, but no luck so far. Something is stopping the gas from going into the burners? What on earth could it be?

 

[glasgowgas]

Many thanks to everybody for all of your suggestions, I have tried all of them, but no luck so far. Something is stopping the gas from going into the burners? What on earth could it be?

you are pretty convinced something is stopping the gas from going to the burner,but have you followed the logic chart to follow sequence?

if you have a multimeter you could check if there is power at gas valve.

power to valve would indicate failed valve

but as others have pointed out you need to start at the start and work through the sequence

 

[Agile]

Many thanks to everybody for all of your suggestions, I have tried all of them, but no luck so far. Something is stopping the gas from going into the burners? What on earth could it be?

Can you describe in detail what you see happening to the pin when the pump starts?

Tony

 

[0308marshman]

Hello, the pin in the differential unit, the part attached to the two pipes, comes under pressure and slides out to push the other pin in the gas valve in.

Kind regards

Eddie

 

[0308marshman]

Hello Everybody,

I have followed everybodys advice, cleaned everything including the differential unit and tested the voltage to the micro switch and the DC Solenoid. There is power getting to the gas valve. All of these seem to be working fine. I fired the boiler up for hot water and it worked fine for about 60 seconds then cut out. I left it off for about 60 seconds and again it fired up and went off again. Does anybody have any suggestions?

Many thanks for your interest and help so far.

Kind regards,

Eddie.

 

[mickyg]

just browsed over thread, so correct me if I'm wrong...
When its not working your saying you have a spark at the electrodes, the pin on the pd valve is operating(when this operates it should be almost impossible to push against it with your finger) and you have power at the gas valve. That would indicate a faulty gas valve, which is very rare on this model. I would check what the voltage you have is, I believe its aprx 20vdc you need. Trouble is your in the realms of gas safety. I would also want to check for pressure fluctuations on the gas inlet when its trying to light, but I can't advise you to do this.

 

[Agile]

Hello Everybody,

All of these seem to be working fine. I fired the boiler up for hot water and it worked fine for about 60 seconds then cut out. I left it off for about 60 seconds and again it fired up and went off again. Does anybody have any suggestions?

Eddie.

When we read the highlighted bits we are left wondering what you were doing and what the boiler was doing.

You say that "YOU" left it off for 60 seconds.

What I want to know is what happens when you turn on the hot tap and stand and watch the boiler without interfering with it for say 5-10 minutes.

Tony