How can I fix my deal Isar combinaton boiler? The radiators keep heating up?

The radiators in our house keep comming on when they are not supposed to especially when we are running the hot tap. It is hard to get constant running hot water and we were told by the boiler people that this is because of the temperature of the underground pipes, Is this true? I also think the batteries have run out on the thermostat and can not remember how to realign this with the boler. I would really appreciate any help with this matter. My husband and children are fed up with luke warm baths and a stuffy house not to mention the cost of my gas on the meter !! Thank you