thank you for your replies, yes the boiler is around 4 or 5 foot which is above the tank.
our boiler man hasnt been in touch yet so i havnt been able to ask him whether it was a non return valve that he has fitted.
i went to my mums today who has exactly the same boiler as me & has had no problems what so ever, i took a picture of hers inside to compare the valves & yes they are different...she has the same valve as what was taken out of ours...i will post a pic of hers.
sarah
Yes looks like you have a bit missing.
Don't get your existing boiler guy back. He has just been wasting your money and time.