it is probably quite old, and the flame sensor might be failing. It is quite common on older boilers, and a simple repair.
I am close to the sea, and when I had one facing the wind from the shore, used to get through them at about 18month intervals, I presume due to salt erosion. Inland they can last years.
If that's what it is, best to get it fixed quickly, because it will only get worse, and may stop igniting, which will be inconvenient in winter. If you do not have a regular service person, ask around neighbours with similar houses. Warm air is not so common in UK now, but there are parts available and people who specialise in it. It benefits from changing the dust filters.