Erratic Circulator Operation

[DAKSY]

Help!
We're coming into a MAJOR cold snap & the circulator on my oil boiler isn't coming on when the T-stat calls for heat...
I am by no means a central heating expert, & forgive me if I don't know the correct terminology,
but there is a Honeywell control - a white plastic box maybe 2x2x3 - mounted in a gray housing - which seems to be actuated by the t-stat.
I believe it to be an operating control. It has the hi-lo settings on it...
If I give the housing a slight tap, the circulator will start running...
The Honeywell item has some numbers on it, but I'm not sure what I'm looking at..
Any ideas on what I'm dealing with, or am I being too vague in my descriptions?
TIA...

 

[Dave T]

I am also no heating expert but you should check the wires by USING CAUTION and wiggling them with the power on and see if one makes the circ flutter, start there it sounds like a loose connection ..Dave