RC1 and WR1 thermostat keeps switching to alarm, despite constant resets!?

Hello,

I hope someone might be albe to help me. I have noticed that my heating alarm LED keeps coming on and this is stopping the heating from reaching its set temperature. I have tried the usual reset with the battery trays and the learn mode several times (with the battery sequence correct) and i have also changed the batteries in the RC1 in the hope that this would solve the problem. Unfortunately it has not! It works for about an hour and then the same problem occurs. I can hit the override and get heat but after a while this also has the same alarm.

Any help would be GREATLY appreciated. The set up and boiler is 18 months old so just out of warranty!