it sound as if it is your heater plugs ok. Have just experienced the same thing with my daughter 1.9 clio. Only 2 of the heater plugs were duff but that was enough to prevent it starting.
If you have a meter just check across ( from engine to top of heater plug where the wire goes on) and see if you have a circuit. Resistance should only be about 1ohm. This will show up any faulty plugs. good luck.
John Patrick
December 2007