Many thanks to everyone. I did have an airlock and I have got rid of it now.

I was only asking about the prices of spare parts because my Potterton Combi 80 is now 5 years old - doesn't seem very reliable and I have been told that I will need a new pump soon. I was told that the price of these pumps would be increasing after April so I should either get one before then or..
the guy also said that the price of condensing boilers would be going up in April and so I should maybe think about replacing the boiler now while the prices are lower.

Any thoughts???

Georgie