Digistat RF3 Wireless heating system

[SL7777]

Help needed please. I have a wireless system over three floors with each floor run by a Digistat RF wireless system. The water runs perfectly and the separate thermostat also runs the all the towel rails in the house which are working great. The presure in the system is spot on. The whole system is 4 yrs old. Since yesterday none of the three floors are responding to the wireless Digistats. The signal seems to be sending on them all and the signal seems to received by triggerring the green lights on the correct receiver boxes. However nothing is happening and I can only get each floor working by switching the Honeywell motorised valves to maual. I have changed all the batteries in the Digistat boxes and also replaced two of the Honeywell motorised valves however the situation still remains? Does anybody have any ideas? It would be much appreciated.
Simon