AN F100 ACCUMULATES ICE FORMED IN THE PITOT BUT RECEIVES NO WARNING OF PITOT HEAT FAILURE.

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XA35Z; 118.3; 4000 FT. ROC APCH AND TWR. UPON ARR AT ROC; OUR NEW HIRE FO DID THE WALKAROUND AND THEN APCHED ME WITH A CHUNK OF ICE ABOUT 1/2 INCH IN DIAMETER HE HAD REMOVED FROM THE FRONT OF THE #1 PITOT TUBE. IT HAD A PIN-SIZE HOLE WHICH STILL ALLOWED AIR INTO THE PITOT TUBE. I DO NOT KNOW HOW MUCH LONGER THIS HOLE WOULD HAVE REMAINED OPEN. MAINT DETERMINED THE PITOT HEAT TO THE CAPT'S PITOT TUBE FAILED. WHAT CONCERNS ME IS THAT THERE WAS NO INDICATION THIS ELEMENT HAD FAILED. I BELIEVE WE SHOULD HAVE GOTTEN A LEVEL 2 ALERT AND A FAULT LIGHT ON PITOT #1. IF THE PITOT HAD CLOSED OFF AIR FLOW COMPLETELY; OUR ARR AND APCH WOULD HAVE BEEN MUCH MORE EXCITING. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT THE ICE PULLED FROM THE PITOT TUBE WAS IMPRESSIVE. HE THOUGHT FOR CERTAIN IT WOULD HAVE PLUGGED THE TUBE; PREVENTING ENOUGH AIR TO GIVE PROPER AIRSPD INDICATIONS. RPTR WAS CONCERNED ABOUT THE LACK OF WARNING OF PITOT TUBE HEAT FAILURE. THE FLC DIDN'T NOTICE ANY DIFFERENCE IN AIRSPD INDICATION AMONG THE 3 AIRSPD INDICATORS. RPTR WAS UNABLE TO FIND OUT ANY FURTHER DETAILS ABOUT THE HEAT FAILURE OR HOW THE HEAT SYS INDICATIONS OPERATED.