Can't light boiler pilot

MrGumby

Hello. I have an ancient swimming pool boiler (no, I'm not rich, just happened to buy a house with a pool!). Every summer, I struggle to get the pilot to light (using a match to the mouth of an ignition tube, there's no spark generator). Usually, there's a bit of dirt or rust blocking the gas supply to the pilot and a gentle tap with something hard shakes it loose. This year, I can hear the gas flowing when I turn the gas control to the pilot position, but when I put a flame to the ignition tube it doesn't draw the flame and light.

Any ideas on what might be wrong?

The boiler's an old American one, can't get parts in this country any more unless they're generic but can sometimes get them from the US.