Boilers are a lot like cars, they have moving parts like fans and pumps which need regular attention. They also have fuel and water sections which can get dirty leading to a reduction in efficiency or eventually a failure.
Your home gas boiler is more important than most people give it credit for. Without it you would not be able to wash (comfortably anyway and in the winter your home would be cold and damp. To say they are the most important appliance in the house is no exaggeration.
Having a regular gas boiler service and gas boiler safety check performed regularly by a heating engineer from the Gas Safe Register (always check the Gas Safe Register online for their credentials) will help to reduce the risk of heating failure.
The time when a boiler is most likely to fail is in the winter, it seems unfair that as soon as the weather turns bad the heating stops working. It is no coincidence that a boiler breakdown happens in the cold weather more, if the boiler has been lying dormant for a few months only operating the hot water and is suddenly turned on it can be a shock to the system. If the water is dirty and has been sitting still for the summer then the pump would struggle to circulate water around the radiators resulting in no heating and could mean no hot water too.
The thermostatic radiator valves can often be jammed after warm weather, "trv" heads automatically close when it is hot and the pin in the valve can stick down which prevents flow. Although this isn't usually checked on a service it is something the home-owner can look out for. See our DIY guide for tips on fixing it yourself, saving costs on hiring a professional unnecessarily.
Different levels of service
Often when a company advertises a "boiler service" they may only offer a safety check, this is below the level of service required by the manufacturers and not sufficient to reduce failure or maintain efficiency. It is worth knowing what you are paying for and what you are getting.
Boiler safety check
Many companies instruct their operatives to safety check a boiler after they have sold a boiler service, this means they do a smaller amount of mechanical checks and spend less time on site. A safety check involves removing the front case to access the gas valve and electronics. The gas pressure is tested to ensure it is within the correct parameters and the flue gasses are analysed to see the emissions. If the gas pressure and emissions are correct then no further action is taken, if the flue shows the boiler is producing too much carbon monoxide for instance then they may recommend a full service to address the problem. If you know that is the service you are paying for then that's fine, lots of boilers can be maintained in that way.
A full domestic gas boiler service should include all of the above but with a bit more time spent checking important parts of the appliance. The gas burner should be removed (or the inspection plate) to inspect the heat exchanger and electrodes. These can be cleaned and the heat exchanger washed, cleaning the heat exchanger on an annual service helps massively to increase the efficiency and reliability of the boiler. A flue gas analyser test conducted on a safety check may not pick up a build-up of deposits which if left unchecked could cause a more serious failure before the next check.