Baxi Combi 105e - flame-out problem?

My boiler runs oK on CH & hot water. However if I shut the CH off from the Controller ,the Boiler keeps running & very shortly the temp in the heat exchanger causes the safety valve to operate - it then shuts down because of "Flame-Out". If it used for HW only using the Pre Heat facility, when max temp is reached i.e. 80degrees, the boiler keeps running & after a short time the Auto-valve operates & the Flame-out flashes.
Anyone with similar problem? Would be grateful for guidance. I should say that in all other respects the unit is OK. Recently serviced!