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.
1 Sharks can smell a drop of blood within a million drops of water or, in a slightly less scientific way, say a teaspoon of blood in an Olympic sized swimming pool and can smell blood hundreds of meters away.  Before sandpaper was developed shark skin was used to sand wood due to the rough dermal denticles.