Apollo fanfare boiler banging

MY boiler for the last year has been getting worse sometimes when you first put it on it goes for a few mins then bangs loudly and then switches off it will then try again to go but will bang again and go out.
We have got cover with a company and they come out and say we need to have the system blown through at the cost of at least 600, I feel that it must be a small prob as it settles down after 30 min s or so and we can start it up again and it will run fine till the next morning when we go through the performance again any ideas any one

Your pump over run stat is not resettin to correct position after use. When boiler turns off the stat senses heat within boiler compartment to keep pump on to dissipate heat. When the heat has gone stat should move internally to position that will bring pump on straight away when HW or heat is next demanded. Yours is not doing this thus when your system next has a demand the pump is not coming on until stat senses heat wihin the compartment and brings the pump on. That is what the banging is, heated water trying to get away from the boiler..... part is still readily available an takes about 20 mins to fit.

thankyou for your advice that sounds like that is the problem our engineer told us that we had a foreighn body in the pipes and it needed blowing out at the cost of hundreds, yet sometimes the boiler runs for days and is fine and then it starts banging we turn it off a few times and then we are up and running again we also hear a lot of gurgling in the rads I thought it might be connected to the pump
many thanks