This comes from the Honeywell site and the aquastat is probably an L7224A since it was recently replaced.
To discourage unauthorized changing of Aquastat® settings, a
procedure to enter the adjustment mode is required. To enter the
adjustment mode, press the UP, DOWN, and I buttons
simultaneously for three seconds. Press the I button until the
feature requiring adjustment is displayed:
LdfLow Limit differential.
F - C°F or °C.
Then press the UP and/or DOWN buttons to move the set point to
the desired value. After 60 seconds without any button inputs, the
control will automatically return to the READ mode.
To use the L7224U in a cold start boiler application, disable the
Low Limit function by pressing the UP arrow button, DOWN arrow
button and I buttons simultaneously for three seconds. Then push
the I button until LL is displayed. Then press the down arrow
button until OFF is displayed.
With the thermostat turned up and the water temperature above the low limit, the circulator should start. If it's a Taco 007, you may have to put your ear directly against it to hear it running, or use a piece of wood against the body of the circulator and to your ear. If the circulator isn't running, that's the problem. If it is running, then the boiler pressure may be too low. It should be at least 12#. If you have 12 pounds and the zones are open, then I would suspect air in the lines.
What exactly happened just before the problem began.