Sime 90 slow start?

My boiler was serviced last December and was working normally.
Now it takes up to a minute to ignite when hot taps are turned on.
The pilot lights up instantly but the ticking continues until main burner fires up. With heating on it's much quicker although heating is also slow starting first time.
My regular Corgi guy is unfamiliar with Sime boilers so I may need to find an expert but don't want to be talked into a replacement as it's only around nine years old.
Some clue as to cost of repair would be most useful