Tdv6 fuel issue

Hello lads, I've a problem with my tdv6. Two days ago I drove my car and parked in garage. Next day when I tried start the engine it didn't started. I called my local mechanic. When he came first what we checked was fuel pump under the seats( which ive chaged changed recently( couldn't find original one and had to install Chinese)) fuel pump was working good, however diesel wasn't coming into the filter. We tried to blow back than and then car started. My mechanic couldn't understand what was the problem. And today when I tried again I had the same problem. Can anyone suggest me what could be the problem. (Plus the funniest thing is today, my dad knocked on top of a pump and it worked, car started) I really love my l322 and don't want to sell it.
Guys, thank you in advance!

If it worked when the pump was knocked, it could well be that your Chinese pump is faulty.

+1 on the possible dodgy pump ! Also check the plug connected to it and make sure there are no bent pins inside the plug.

Thank you guys. I changed secondary pump under the rear passanger side and tbh it works perfectly. And sometimes i think car got more power than before.