The majority of boilers only modulate 5 or 6:1 but yours is 10:1 so maybe to replicate these boilers increase the min output to 25/30% (5-A3) and see how it goes, can't do any harm. and can always revert.
I have asked the question of the installers (still waiting an answer) and I was thinking of having it changed from 10% to 20-25% as a test (can put heat on full and see how it performs)
I can eventually manage to get the temerpature to 60 degrees if I let the boiler come on for 3 minutes min time and off for 7 minutes (it cycles every 10 minutes) and this at least lets the radiator get warm (at the expense of gas) after about 4 cycles (so 12 minutes gas)
Hopefully if the change to 20% ish makes the boiler start modulating higher this will help the Evohome system and I can probably back off the 3 minutes to 2 (it should eventually learn what is what) and also get the heat up to 70 degrees quicker when the zones are fully open.
Thanks
Colin