You have got off lightly.
A collegue called them out on Boxing day last year. They couldn't even send an engineer until the follwing Thurs (I think boxing day was Sat/Sun IIRC). Engineer couldn't fix it, ordered parts and they had to wait until the middle of Jan for them to come back and fix it.
I have cover with a local plumber. Costs me about £120 per year (which I think is a fraction of BG). They come and serivce annually within that price and the one time I have called them they were here within 2hours (and it was an evening call). They were not able to fix it there and then because they needed a part which they couldn't get at 8/9pm. But they had fied it by lunchtime/early afternoon next day.
Obviously I can't recommend them because you are not local to me. But I do recommend finding a local recommendation.