Drayton Digistat RF1?

Have come home from an extended holiday to find no heating. Stat set at 15c to come on when house cold. Stat showing 13c.
Found boiler had lost pressure so topped up.
Following morning still no heating receiver only had red flight on, pressed button 2 and green light came on and heating fired up. But next cycle same problem. Have replaced batteries with new ones, still same. Switched power off and left a while switched on and on receiver pressed and help button 1 followed by 2, red light flashed and then went out. Replease both buttons after a while, but still no joy.
Any suggestions to solve and repair or just replace?