Right then. I've an update. I'm convinced now this is an internal controller issue as the only way to get the heating to work is (as previously suggested) link L - F.
Doing L-R did nothing. I'm not very familiar with the cycles but I can only best describe it as a 3 - 4 min loop of the pump circulating the heat around the circuit and reaching a max of 40C on the LCD.
Boiler would shut down, go through the motions then rinse, repeat. Took the chill off the house but only slightly. Rads barely even warm to the touch. Incidentally, this is no real fix as the cycles were not reliable (halted intermittently and could just hear fan for ages) so had to switch spur off/on to restart process. Proper weird.
It's evideny clear now the C/H in this property has not been checked or run for literally....months.
I also realised when NOT connected up this way, I can't with the mode button even manipulate or adjust the HW temp. Again just to clarify, the - & + do nothing.
If I hold mode for 2 seconds, nothing happens. If I hold for 5 secs, if I'm lucky, the LCD will greet me with the tell tale flashing rad symbol but with 'off'above it.
Opening a tap and even then, can't adjust the temp.
Also, the status codes were such as S30, S31, S97. No F codes present.
I've checked all the connection thrice and there's no signs off anything missing or loose.
Soooooooo, I reckon it's a new PCB?
Does the above make any sense and have I got that right?
I do hope I've cleared things up and thanks for everyones advice. I just want this stupid boiler working. I swear this thing is the Devils offspring and it's taking the **** out of me!