How combi boilers work

Combination boilers, or combi boilers as they are called are the most common boilers in the UK. They are designed to provide instant hot water, as well as heating up all the radiators.

If the temperature in your home drops below your pre-set level, the room thermostat sends a signal to the boiler to fire up so that heat can be directed into the central heating system and out to the radiators. The opposite happens when the thermostat detects the pre-set level has been reached the boiler shuts down

When you turn on the hot water tap, water is heated inside the combination boiler, which then flows to the relevant tap. The advantage of a combi boiler is only the water needed is heated.

Control valves inside the combi boilers operate in different directions, either letting the water flow through the heating system or diverting it to a to water tap, as required, but never both at the same time.

Combi boilers require sufficient mains water pressure in order to deliver a good water flow rate; low mains water pressure means hot water will merely trickle. If your mains water pressure is low or you have more than one bathroom, installing a booster is an option to provide ideal shower water pressure.

It is also important to ensure that the heat output of the boiler is correct for your needs. Combi boilers generally have two heat outputs: one for domestic hot water and the other for Central Heating. More effort and hence more heat is required to produce hot water than to heat a home through the radiators, so it is usually the hot water output that determines your choice of combi boiler. Call 020 7350 2511 and one of our engineers can help you determine the best options for your boiler and heating system.

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