If you are experiencing a boiler working ON and OFF, having to top up boiler pressure almost every day , then your boiler might be suffering from expansion failure .
We normally solve this issue before it even starts simply by re pressurising your combi boiler or system boiler expansion vessel during a routine annual service.
Expansion vessel is like the lungs of your system. Without it in good shape, your system suffocate and causes the rest of the devices to malfunction.