difficulty firing up a combi

[michaelangelo7]

My five year old Worcester Bosch 350 sometimes has several attempts to fire up when the room stat calls for heat.I can hear the main flame come on then after about 10 secs it comes on again.(Pump keeps running regardless) Sometimes it wont light and I have to turn the room stat off and let it have another attempt. It eventually fires up but it's annoying to keep coming home to a cold house. Any pointers please? michaelangelo7

[BigWallop]

It needs properly serviced. It could be a build up of dirt on the burner and surrounding detector devices, like the pilot flame coupling etc. So get it cleaned and serviced properly and it should be OK.