Overriding the timer will most likely solve your issue. If the controller is not telling the boiler to fire, it's irrelevant if the stat is, otherwise your heating would fire all the time.
It depends what kind of timer you have, if it's an old school rotary one, there will likely be a switch with a O, I and a little clock. Switch it to I, or you could pop the tappets for 11pm in and see if it fires at 11.
If it's a digital one, there will likely be a button/switch to switch from timed to 'constant' or 'run' or maybe 'override'
If you can't work it out, let us know what make/model it is, I'm sure someone will know the answer
It depends what kind of timer you have, if it's an old school rotary one, there will likely be a switch with a O, I and a little clock. Switch it to I, or you could pop the tappets for 11pm in and see if it fires at 11.
If it's a digital one, there will likely be a button/switch to switch from timed to 'constant' or 'run' or maybe 'override'
If you can't work it out, let us know what make/model it is, I'm sure someone will know the answer