Quote Originally Posted by MkWangus View Post
I should also add the sub tank light is on, I've checked for fault codes but there are none. Disconnected the battery for an hour and reconnected it which fixed it but next morning it was there again.

I'm guessing the switch for the sub tank is faulty as it doesn't click when pressed just feels soft with no resistance and minimal travel and also doesn't light up. Is this normal or is the sub tank switch meant to click on and off and light up?
Possibly a dirty earth connection. Run another earth lead from the trans to the chassis and also clean up the other earth points on the battery and the one from the starter battery down to the chassis.