Have had a shot of a works van for the last 6 month so my vrs tdi has been sitting a lot only used once or twice a fortnight, a few weeks ago it was struggling to start, was turning over but wouldn'u go, putting my booster pack on got it to start ok. I thought must be the battery so replaced the battery a few nights ago and still didn't want to start. It was after a few minutes of not trying I turned it and went first turn. I couldn't remember seeing the glowplug light when I was first trying and tried again tonight, there was no light and just kept turning but not starting, left it a few minutes - turned the key and the glowplug light lit and started first time. Had a Google to try and find the problem and few things saying relay 109. How do I find out if this is the problem, just replace it and see if it cures it or is there any tell tale signs? 

It looks like there isn't a relay 109 on mk2 and that was on the mk1 octy, anybody any ideas what could cause this on a mk2 tdi? Thanks in advance