Common rail diesels such as the HDi do not rely on the glow plugs for cold starting, in fact the primary purpose of the glow plugs isn't for cold starting at all, although they do switch on for preheating if the outside air temperature is below about 5° Celcius.

The glow plug’s function is to reduce noise, as well as to give improved emissions and running when the engine is cold. Common problems on HDi’s are in-tank fuel pump failure. Remove the fuel filter housing and check for metal filings. If you see some it’s a sure sign of a pump that’s failing, and also the main pump may be suspect too. Common rail fuel pressure needs to reach 10,000kpa before the engine will start, and if you have a worn pump this pressure may not be achieved.