Vaillant Ecotec plus 824 with no central heating?

Please help!!

We've been in this house for almost a year - so I'm not sure when the boiler was installed but I have all the instructions etc - it is a Vaillant ecotec plus 824, and it worked fine over last winter. It also worked fine once or twice last week when I switched it on manually. For some reason today it isn't triggering the heating at all, no matter which way I try and switch it on. I have completely reset the thermostat controls (drayton wireless rf3) - it's all set up correctly and the signal is being received by the unit under the boiler (nice green light), red flashes when signal being received then back to green. However the boiler displays S.30, which I believe is 'no heating demand from thermostat'? The hot water is working fine, and the test setting for the heating is ok too (pressing + & - together), in that the boiler and radiators come on. The only fault codes I found are F.22 which must be to do with installation so I have no clues! I've tried the timeswitch being on, timed, timed with all the tappets pushed in....aargh.

Anybody got any ideas? I would be really grateful for any help!