I've got the same problem. Iflo wireless thermostat, & a reciever next to the Combi. Hot water is fine but the central heating won't turn on when demand is required, unless I turn off power to the boiler/reciever and leave it off for a few minutes. When power is restored and demand for heating is made it works. I get the green light on the reciever and the flame icon on the wireless thermostat too even though the boiler hasn't fired up.
Rb, September 2013