how to bleed air from boiler?

[kggkgg]

Hi
first time posting here.

Over the summer i drained flushed and refilled my central heating. Since then the hotwater delivery has been slightly unreliable (combi boiler, worcester 35CDi II) with the flame cutting out from time to time. Heating is rock solid. Of course i fully bled the system and all rads are hot.

I rang Worcester and they said that there may be air or a blockage in the primary side causing the boiler to overheat and thus to cut out.

hoping this may still be an air problem , how do i bleed air from the top of the boiler. I noticed a black thumbscrew which when turned nothing happens (no hiss of air). Also a little red cap which i have not yet opened.

any help appreciated so avoid a massive bill for calling out .

Keith

 

[gas_man_gaz]

by your descripition the red one is the test point for the immisions and the black one is the cap for the auto air vent. it should vent the air auomaticly but sometimes can block up, but if ya heating is working ok iam guessin it isnt a fault with air in the system anyway