Goodday (probably not because your boiler doesn't work and you just had to take a cold shower :) )
I have TurboTEC pro boiler, yesterday it was fine, today it was alternating between F22 and .2 bar, and the pressure gauge indicated about 0 bar.
If you experience the same problem, you might want to try my solution.
First, turn off your boiler by turning the IO knob to O.
There is no internal tap to fill boiler. Under the boiler are many different water pipes. I figured that the outer two (thick ones) must be the 'in' and 'out' of the heating circuit.
one of the middle three must have a manual lever which, when opened, fills up the boiler. Just try them all. You can hear the sound of water flowing into the boiler, and see the pressure gauge slowly come up. Undo your changes if it is not the right one.
Stop this process when the needle of the gauge is about 2 to 3 mm into the gray area.
Close the filling taps, and restart your boiler by pressing ctrl-alt-delete (no just kidding just turn the IO knob to I.) If there are no other major malfunctions, the boiler should do a self-check, and start burning again within the minute.
As of what caused this is still a mystery to me, as i know absolutely almost nothing about boilers. It could have been a pump and/or sensor failure, whereas the build-up pressure would likely slowly fade away into the overflow, until there is no pressure at all left in the system.
Anyway this worked for me, hope it works for you too.
Have a good one.
Gromit, August 2013
