How do I override the digits at RF wireless system on my firebird oil boile?

I have just moved into a home with a firebird oil boiler. This has a remote digits at RF3 wireless timer and temperature system. It is apparently about 15 years old. Yesterday evening the radiators went off outside of the normal time despite the required temperature not being met and we have been unable to get the radiators back on. The boiler is producing hot water. I have looked at the instructions and there is no battery light to indicate replacement batteries are required and I have had the battery compartments out to ensure it is not in learning mode. Can I override the system on the boiler?