Probably gonna cost you. You shouldnt fiddle around with a gas appliance if your not Corgi registered. Nasty things can happen and it against the gas regulations for obvious safety regulations.
Difficult to say but if the light went out and wont relight, could be as simple as a thermocouple, or as complex as replacing it's innards. Sometimes it can be a safety measure if the pressure in the pipework is too low for the boiler to operate safely.
At least the weather is getting warmer, so you can manage without heating. But watch out for the cold showers
