Riello rdb1 not cycling beyond purge

[readingyoufives]

Hi guys, will be grateful for your advice. Riello rdb1 in Grant combi. When boiler has been switched off for several hours on start up burner cycles properly and boiler runs OK. Having reached operating temp with heating and hot water all fine, on demanding heat once again the fan motor runs but start cycle goes no further and there is no lock out after 12 secs, motor just keeps running. Isolate from mains and leave for several hours and starts OK again. Burner has new pump, control box and capacitor. Any thoughts? Thanks for your help

 

[SimonG]

That will be the photocell.

 

[readingyoufives]

That will be the photocell.

You are spot on Simon, thanks. Just disconnected cell at control box and burner cycles through properly then locks out after firing for a few seconds. Reconnected it and fan only as before. You are a star, cheers.