baxi solo wm70/4 pf-boiler cycling on and off after1/2 mins.

[gerfitzp]

i have a baxi solo wm70/4/pf which is cycling on and off. i have changed the pcb,gas valve(pressures checked with manometer) and boiler thermostat. i have not changed the pump overrun thermostat. how do i check the pump overrun stat before changing.is it a voltage ,continuity or resistance check.i would appreciate any assistance.

 

[namsag]

What sometimes happens is when the air pressure switch gets old and wears it is not strong enough to stay made and causes the boiler to cycle, also check tubes to switch have not split.
Also a dirty pilot getting pulled away from electrode when main burner comes on can cause this