By Mohammed Miah, Gas Safe registered heating engineer
Combi and system boilers are the two most common types fitted in UK homes today, and they work quite differently.
Combi boilers
A combi (combination) boiler heats water directly from the mains, on demand, no tank or cylinder needed. That makes it compact and space-saving, and you get constant hot water pressure straight from the mains. The trade-off is that hot water output is limited by the boiler's size, so running two showers at once can affect pressure.
System boilers
A system boiler heats water and stores it in a separate hot water cylinder, ready to draw on. This means it can supply multiple bathrooms at full pressure simultaneously, which makes it a better fit for larger homes with higher hot water demand. It does need space for a cylinder, and hot water is finite until the cylinder reheats.
Which is right for you
Smaller properties with one bathroom and lower simultaneous hot water demand usually suit a combi well. Larger homes, especially with two or more bathrooms, tend to get more consistent performance from a system boiler. We'll talk through your household's actual usage during a free estimate and recommend whichever genuinely suits your home.
