[Giles1234]

I think they can go at anytime, regardless of whether the pump is running or not. There must be a safety blow-off valve otherwise we'd be driving around in a potential bomb!

I had one replaced about a month ago. The service manager said that they are now replacing burst pipes with upgraded pipes. So Volvo must have identified a manufacturing fault with the original pipes that is causing them to fail, rather than system over-pressure bursting them.