Fixing the furnace

As morning > afternoon, the temp in my house fell to 61 F.  I felt no heat from the radiators.  Pumps were running cold water through the system. 
Into the basement to inspect the boiler.  I touched cold pipes that should have been hot.  I flicked the power switch off, then on, the boiler started up and then fizzled.  Recalling a $100 visit by a repairman, I pulled the hose under the firebox of the boiler and began to poke into the hole where it connected, and little bits of hard water deposits fell out.  I though water might come out, so I tried to undo the nut around the hose connector without success.  I turned on the boiler and this time it stayed on. I watched the needle on the thermometer rise to 120° and then to 145°.  Case closed.