Sorry to butt in,my pedal is very soft but goes hard when I give it one pump...I have an intermittent BAS/ESP light. On my friends diagnostics it said brake light switch and diaphragm on the booster (servo). The pedal symptoms are just like air but bleeding doesn't get any out,I'm going to use his power bleeder but I need to change rusty brake pipes first. (MOT due mid December)...Is this non-return valve you refer to this diaphragm? Part# A0015401517..Cheers.This sounds like a 'servo' problem. i.e., the Brake Assist System (BAS) that your brake pedal is connected to. A non-return valve within the brake booster (A7/7) should maintain a high pressure in the line.
What happens if you 'pump' the pedal?
No. The diaphragm is something else.Is this non-return valve you refer to this diaphragm? Part# A0015401517..Cheers.