Sabre combi boiler canstantly ON?

Hi
Can anyone help me please I have a Sabre Combi boiler and my problem is this. My heating is constantly ON no matter what I do it is controlled by a Sunvic wireless thermostate. I have done everything on the thermastitic side and am sure that the problem does not come from there . The burner is constantly ON as I say even when the green light indicatore is flashing so it is not demanding heat but it seems as if the burner is jammed on(only a thought on my part). I have turned of the system and restarted it but as soon as it gets power you hear the burner starting up. I have also got the correct water pressure set correctly between 1 and 1.25 bar