Vailiant boiler banging on start up

[Timmy2024]

Hi all,
I have a vailiant turbo max
When running constant overnight I kept waking up to low pressure error, although it was reading about 1.5 bar.
Anyway I decided to add water to see if it would make a difference. I'm a complete novice in boilers and turned the grey dump valve I filled the water back up to 1.5 bar.
Since then I get 4 or 5 loud bangs everything it turns on then stops and heating works as normal.
I looked through forums etc but I have no P0 (only p1 and p2) so can't purge system. I've bled radiators. So 2 questions.
1) How can I make banging stop, am I missing something? How do I purge pump?
2) just to be sure, the cold water supply needs to be closed and the CH return needs to be open (I messed with those two and just want to make sure I've turned them right, I assume lefty loose, right tighty)

Thanks!!

 

[DP]

Get a boiler repairer with fault finding skills to look at the boiler. Service in the first instance
You will likely not have the tools or the instruments to carry out the task