Vaillant sine t3w would not fire up

[Bunnyman]

Go away tony ffs, you say you have had wax stats everytime for your own customer for the last 5 years? You either have few customers or millions of wax stats? And op, as said many say that they have stock but dont, you may find some used stock on ebay

 

[Dancan]

Yes Bunnyman you are right. There are many sellers on ebay who stock the parts for this model.

I managed to find the fault. It is in the differential valve. I removed the differential valve(pic attached), cleaned it ,diaphragm was in a good condition, the pin inside was rusted, so i cleaned it and applied WD-40 to remove the rust and greased it with it. I put it back together and fired up the boiler and ran the hot water tap but instead of water ,the radiators were heating up. When I close the tap and run it again, the boiler would not fire up. I removed the differential valve and cleaned it nicely and screwed it back , fired up the boiler and it worked when i run the hot water tap but when i close it and run it again, it wouldnt come back again.

Do I need a new differential valve?? or do i buy a silicone grease and apply it on the pin and try that first? Which silicone grease would you suggest?

Thank you

 

[Dancan]

Update - The boiler is working fine for now. I greased the pin on the differential valve and no problems so far. Thank you guys for your suggestions.
The air vent(pic attached) needs replacing but it is too rusty and would not unscrew. Any suggestions on how to go about it?

 

[Dancan]

@The831Bunny Thanks for the reply. Already fixed that issue. The air vent(pic attached) needs replacing but it is too rusty and would not unscrew. Any suggestions on how to go about it?

 

[ianmcd]

That part is an easy fix and readily available as it is a common part but doubt that is your problem , just close the vent cap and it is just a bit of metal then

 

[Dancan]

@ianmcd It leaks water sometimes, so it needs changing. I have bought the part but the one on the boiler is rusted and would not come off easily.

 

[ianmcd]

they are used in most boilers and it is only the size of the connection that determines which one you need , it is called an automatic air vent AAV, sometimes an automatic air bottle AAB, but basically it is a float operated mechanism where if air is present then the float drops and allows the air out of the vent , until water replaces the air and closes the valve, they leak for fun , they are very unreliable, just get any one with the same thread and connection size, as already said doubt very much if that is your problem , @Bunnyman chipped in a few times on your post , PM him and see if he can help you out , he is the man for your boiler, he has the experience and may have any parts you might need

 

[Dancan]

Already purchased the AAV. Looking for right method to unsscrew the rusted AAV on the boiler.

 

[AGAS]

Just unscrew it the body that is remember to drain drain down you have stripped the differential but your having problems unscrewing an aav

 

[Dancan]

@AGAS As i said it is highly rusted and would not come off and i do not want to ruin the thread but anyways I will try and update this post. Thanks

 

[Agile]

The body is made of brass but screws into a cast iron body.

They will usually unscrew OK but I suppose might sometimes shear off.

If they are both the same type the top part can usually be unscrewed and changed over.

 

[45yearsagasman]

Tony will have some,,but he's keeping them for his own customers