Reset Button. Most boilers have safety devices built in, so if these are tripped a simple reset may get your whole system working. The reset button is normally on the front of the boiler. Sometimes it's a dial that needs resetting to zero and turned back on.
A typical diffusion constant for a medium-sized molecule in water is about . If we want the smell to travel a quarter mile, or a little less than , we get a speed of. This speed is fantastically slow, and says that it would take ten million years for blood to diffuse out to a shark a quarter mile away.
A few things that could attract a shark to a human is blood (which can also cause a feeding frenzy) and a human paddling out to catch some waves (surfing) looks like a seal so that can also attract sharks, however sharks have a keen sense of smell so it is more likely that blood will attract sharks.