Vailant Sine 18 Combi

[Aljay]

Needed to change the diaphragm in the water section of the above boiler so whilst the system was drained decided to change the diaphragm in the differential valve at the same time. Big mistake (if its not broke don't fix it). Now the boiler won't flash up, the new diaphragm is not pushing the pin out with sufficient force to operate the gas valve!!! Stripped everything down and checked all was clear ie the two tubes and also cleaned the venturi. Couldn't find anyting wrong but still no joy. Any suggestions? By the way I had a spare (old) pump which I've put in but still no go

 

[namsag]

Get ALL the air out as even a little left in these will stop everything working right .There is a bleed at the top of the heat exchanger and also at the top of the calorifier

 

[spacethegas]

namag is right its air & can be a pain to remove.
lots of backfilling, starting & stopping pump, bleeding, cracking joints etc.

 

[Aljay]

I've bled the boiler from the heat exchanger and the DHW calorifier stopped and started the pump a dozen times. The force behind the pin is now much stronger but still not enough to move the pin on the gas valve so I'm sure you are both right that the prblem is air but I'm at a loss as to how I proceed, not sure as to this "back-filling" or "cracking joints"especially with a full system.

 

[Gasguru]

Are you sure the auto air vent on the pump is working?...they often scale up and block.

 

[Agile]

Needed to change the diaphragm in the water section of the above boiler so whilst the system was drained decided to change the diaphragm in the differential valve at the same time.

Well thats not logical!

To change the DHW diaphragm you only drain the DHW.

There was no need to touch the heating circuit.

The old adage, dont fix it if its not broken comes to mind!

Tony