Potterton combi performa 24 heating not switching off?

Room stat calls for heat and boiler fires up. yellow light comes on boiler. When room temp has been reached, flame lcd display on room stat goes away but boiler keeps working. Yellow light goes out on it's own after about an hour. Can turn off heating and yellow light by turning off boiler. Turn on boiler again and heating and yellow light now off. Using a wireless room stat.
Hot water working fine.