There are several reasons why boilers can become less efficient over time:

1. Sediment build-up: Over time, sediment can accumulate at the bottom of the boiler, which can interfere with the heating process and reduce efficiency.
2. Malfunctioning parts: Boilers have many different parts that can wear out or break down, such as the burners, controls, and heat exchanger. If any of these parts are not functioning properly, it can reduce the efficiency of the boiler.
3. Lack of maintenance: Regular maintenance is important to keep a boiler running efficiently. If a boiler is not properly maintained, it can become less efficient over time.
4. Age: As boilers age, they can become less efficient due to wear and tear on the various components.
5. Incorrect sizing: If a boiler is too large or too small for the space it is heating, it can be less efficient. It is important to choose a boiler that is properly sized for your home.

There are several benefits to upgrading to a more efficient boiler:

1. Energy efficiency: A more efficient boiler will use less fuel to produce the same amount of heat, which can save you money on your energy bills.
2. Lower carbon footprint: By using less fuel, a more efficient boiler will also produce fewer greenhouse gas emissions, which can help reduce your carbon footprint.
3. Longer lifespan: Modern boilers are designed to last longer than older models, so upgrading to a new boiler may also save you money in the long run by reducing the need for costly repairs.
4. Improved comfort: A new, high-efficiency boiler will heat your home more evenly and consistently, which can improve your overall comfort.
5. Potential rebates and incentives: Many utility companies and local governments offer rebates or incentives for homeowners who upgrade to a more efficient boiler, which can help offset the cost of the upgrade.