As the man said before....

"The pump is a usual suspect, you can feel if the pump motor is spinning or not. "

1) Try using a length of radiator hose as a stethiscope and place one ond on the Circ Pump and your ear to the other end...you will hear if the pump is turnong when the Heat switch is engaged.

2) Place your fingers on the outside of the Circ. Pump...you will feel the vibes if its working.