I have had the same problem over the last couple of weeks, the condensate pipe was freezing up out side, we lagged it etc, and it's normally fine and fires up again soon as we clear the pipe. But this time, we cleared the pipe, a good dose of water drained from the flexi pipe on the boiler into a pan when I disconnected it from the external condensate pipe also.
Now every time I fire up the boiler it boots, then try igniting (not flame symbol appears on display) and then error 12. Again and again, left the condensate pipe leading into a pan but nothing has been coming and and that is definitely ice free there.
Any suggestions? I've tried warming the boiler with a fan heater just to make sure it's all ok. Other than waiting for the weather to warm, I don't know what to do and we can't get an engineer out till Monday :-s
Thanks 🙂