I am with SafeGasInstall on this one.
The OP seems to be contradicting himself.
- He says he doesn't need to explain why the plumber went there, then says he was sent there to inspect the boiler
- He says the plumber is not interested in 'servicing' the boiler, then says it will be sorted once he decides .....
I am convinced if the OP is willing to get a second opinion, the next RGI who attends will find more than NCS. All the same, I wish the OP all the best for the house purchase.
If you find that your 12 year old car is giving you problems, do you wait till you're on the M25 and it packs up b4 you get it serviced or replaced or do you make a decision to have the car replaced? I know what I will do. I will have it replaced.
Let us say for simplicity sake that you find someone who is happy to charge you £400 for labour & parts to resolve the flue issue. Two months later, the PCB needs replacing. Another two months & the pump or fan needs replacing. Before you know it, you have spent £600+ just within SIX months. Do you consider that VFM? I don't.