Just measure the low voltage at the termnal strip of the Boiler : R and
C....then again at the terminal strip on the Boiler : W and C ; Do this
when the thermostat is calling for heat. There shouldnt be much
difference between the two readings but there is typically a small
voltage drop ; So long as the voltage between W and C is no less than
approx. 22 volts ... you are within safe and proper conditions and you
can figure you arent loosing an excessive amount of voltage due to loose
or poor connections. Hope that helps.