Potterton Profile 80 - lowering control unit makes it work!!?

Boiler wasn't igniting but fan appeared to be running ok. Heating engineer had a look and discovered that tilting down the metal plate holding the pcb and wiring made the boiler start. Pushing it back up and it cut out. Tilt it down and it will start again.

He left saying he would speak to Potterton about it, but he has since disappeared off the face of the earth. At the moment it still works for a few hours tilted down, then cuts out, but fires again if left to cool right down, or if pushed back up then tilted down again (to about 45 degrees). As you tilt it back down you can hear a click, then it fires.

Anyone heard of this? How should I proceed? Thanks.