I wouldn't expect a pyracantha to be a danger to foundations, they're often wall-trained on houses. If it's very close to a drain it might cause problems though.

If its not serving any useful purpose and you're not particularly attached to it, I'd be inclined to take it out - they can form pretty big roots, and, as Annie says, the real worry is the presence of the drain and underground pipework. If its in a paved area, cut it right down and drill into the stump and treat with SBK. On the other hand, it's obviously been kept as a small hedge, so its root development will be much less because of that, so as long as you keep it trimmed, it'll probably be fine - clearly its been there a long time and hasn't yet caused a problem.

I've never heard of a pyracantha damaging drains. We had one growing on the downstairs toilet wall with no problems.

My thanks to Annie, Bamboo and Steragram. Its obviously a finely balanced matter, at present going slightly in favour of leaving it alone!