rads come on but heating is apparently turned off!?

[knownothingatall]

Halstead CBX32 boiler fitted Jan 2007 - serviced every year. Have moved out of house since, couldn't sell so rent it and tenant says radiators come on even though he's turned the central heating off (hot water is on.)
I'm about to drive over and look at this - only thing I can think of is that he hasn't turned the Central Heating to Standby and has just turned it down. Could it be anything else?
Obviously I will call a Gas Safe Plumber out if it isn't a control that needs to be adjusted - but don't want another big bill if is has been set incorrectly.

 

[davebgas]

Diverter valve is passing....

 

[knownothingatall]

Thanks Dave - I forgot to mention the no 2 led warning light is coming on too - which the manual says is because the flue gas is too hot. Could it be something as simple as the rads need bleeding and a serious air lock is causing the problems?