The plumber/engineer came today (two days early, can't complain!) and did pretty much what Aquaheat said, the thermostat receiver wasn't sending any signal through to the boiler, the timer is still working, so he changed the wiring to let us control the temperature directly from the boiler, and will install a more reliable one at a later date.
Thanks for the help, I hope this thread will be handy for anyone else stuck in my position in future, heating is such a pain in the @$$, something we take for granted until it breaks, especially when you have elderly and vulnerable people in the household, so it's great to have these forums to fall back on. Cheers.