Since you're saying circ' problems you mean the lights are: (left to right) ON - FLASH - FLASH?
If so then yes, first check circulation, feel the system pump- is it vibrating? Is there water in system, can you hear water flow or air movement in pipes when boiler starts with a demand for heat?
The casting thermistor doesn't fail that often, usually after someone has been working on boiler and damaged it with the fan hood.
Have you had any work done, any prior symptoms, will it run at all- after reset?
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