What does the glow plug light on my Volkswagen Passat indicate?

I bought a used Volkswagen Passat Estate in Oct 2016 (124,000 miles on the clock) with a 12 month warranty. On the first motorway drive the glow plug warning light came on. I returned it to the dealer to fix it but it he can find nothing wrong. It came on again last week so I pulled into a service area and stopped it, it didn't come back on when I continued my journey. What is the reason for this?
The glow plug light indicates that the EGR valve is either clogged up or has failed.
Answered by Honest John on

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