drayton wireless room stat?

I have a drayton wireless room stat controlling the
heating. the boiler is an ideal icos. The trouble i have is that i only get heating when it feels like it. The boiler fires up every time i ask for hot water, but call for heating and you get nothing. The scr receiver flashes when the stat is changed but thats as far as it goes. I have found though that it tends to work more often if the hot water has not been on.
I have changed the mid position valve, the programmer and the cylinder stat but the symptems still persist. Is it the scr receiver not sending the signal to fire up to the boiler possibly?