URGENT repair of Gas Central Heating

Braemar furnace TH420 fitted in 2009 - has suddenly stopped working, digital displays still work (see photo), you can set the temperature, the flame symbol and fan symbols come on for only about 30 seconds and no heat is produced. Installer can't come out till next week, if you can get out sooner, please let me know.....it's cold! Onewa Road (motorway end)