Boiler or Thermostat?

When I switch on my boiler it fires up but the fan starts, the ignition light fires up the gas burners and the radiators start to warm up, then after about 10 minutes the gas burners go out and the radiators start to cool down.

After messing around with the temperature gage on the boiler turning it up and down repeatedly the gas burners start up again but again after 10 minutes or so they again go out.

Is this the boiler or is it a fault on the thermostat?