Vaillant vuw hw problem

[ollski]

Got a bit of a Wierd one, turn the hw tap on and the white rocker switch does not move at all but if the tap is turned off and then on again it will run every time. Leave it 10 mins and it will fail again the same way. Have replaced the complete bottom section of the valve and fitted a complete service kit (spindles/ packing glands / o rings etc) and it still does the same.

 

[petit_pablo]

A dead leg somewhere stopping the pressure differential perhaps?

 

[ollski]

Couldn't see one and no work been done on the system recently.

 

[The831Bunny]

Take the pump out and veiw the spindle rising (or not) through the DV port. It may give you a better indication of the problem. The white lever may be partially broken too. Other candidates could be blocked connecting port above the Venturi, a bent or seized DV shuttle in the top section, a passing shower somewhere down the line, or a broken cage in the bottom section, a blocked Venturi in the bottom section. I'm leaving out the obvious diaphragm etc but it does sound strange.

 

[ollski]

Cheers bunny I'm just going to swap the complete valve like I probably should have done to start with!

 

[The831Bunny]

I'd keep hold of that bottom section as a spare 'cos you may find you'll need it one day

Also when replacing the DV, note that the pump screws are NOT all the same. The short screw above the pump must only be used there. Use one of the longer bottom two, and it will puncture the pipe behind if you wind it in hard enough

These boilers are reliable except for dhw problems...

 

[Bunnyman]

U say u fitted the complete kit, did u change the plastic arm as well?

 

[ollski]

U say u fitted the complete kit, did u change the plastic arm as well?

No, everything but that and I must admit that has been bugging me.

 

[Bunnyman]

The arm comes in the kit? An MUST be changed that's the main bit that fails