Combination boilers are currently popular in Great Britain. According to eastrenfrewshire.gov.uk, they supply you with heating and hot water "on demand" and without a hot water tank. They give you exactly as much hot water as you need in that moment, so you save money and energy. However, "combi" boilers, as many call them, also have clear disadvantages.
Combination boilers can be difficult to repair if they break down, due to their complex structure. According to miketheboilerman.com, fewer repairmen are willing to attempt to fix them because it takes too long, and this could mean more cost for the consumer who seeks repairs on his combi.
According to miketheboilerman.com, combis have a tendency to scale up. According to process-controls.com, scaling is a coating that develops on surfaces once they've come in contact with hard water. These deposits can plug up the inner piping and interfere with the performance of the boiler. Buying descaling equipment every two or three years can become costly.
According to miketheboilerman.com, the water pressure on sprinklers connected to a combi boiler can drop. In the winter, when no one is watering his lawn, the sprinklers work well. Once summer hits, however, and people begin using the water systems to water their grass, the increased demand for water creates stress on the system that can cause your appliance to shut down.
Flue Exhaust Gases
According to combiboiler.org, if you install a combination boiler, your flue exhaust gases may increase in weight. The temperature of these gases decreases, and a plume can result from condensation. These gases, now in liquid form, can create wet areas near the outlet that can spread beyond your home and affect others' properties, and can even be harmful to those passing by your house.
Hot Water Lag
As combiboiler.org points out, an annoying lag in hot water production can happen as you attempt to take a shower. When other people are trying to shower as well, it lowering the water pressure of your unit. In fact, if usage becomes too intense, it could result in the total shutdown of your combi boiler for a few minutes.