I have a Potterton Envoy Flowsure+ which intermittently cuts out after it fails to ignite after 3 attempts. It fires up on pressing the reset botton but then cuts out again a few hours to a few weeks later. potterton engineers have looked at it and replaced the hot surface ingnitor, the flame sensor, and on one occasion said it was a loose connection. They have not replaced the PCB( although I don't know what PCB stands for!) However the problem with intermittent cutout persists. Can anyone help?