Combi Boiler Installation FAQ

A gas combi fitted is €1,800–€4,000, typically about €2,700. An oil combi is €3,500–€5,890. Converting from a cylinder and tanks is €3,400–€4,800.

One day for a combi swap. Two for a conversion from a cylinder, or if the boiler moves.

Gas work only goes to a Registered Gas Installer (RGI). Oil combis go to an oil technician. You get a certificate after gas work.

No. SEAI has no grant for a new gas or oil boiler. Its €700 heating controls grant can apply in a home built and occupied before 2011.

Not well at the same time. Homes with two or more bathrooms in use together often do better with a system boiler.

A new boiler carries the maker's warranty, usually on condition of a yearly service. Ask about the installer's guarantee on the fitting.

Yes, all 26. Pick your county's page for how homes there heat and what a combi costs.

A standard 24 kW to 30 kW combi boiler heats water on demand for one high-flow shower at a time. Opening a second shower or bath tap splits the flow rate between both outlets. Homes with two busy bathrooms running simultaneously either choose a high-output 35 kW combi with strong mains flow (18 L/min+) or opt for a system boiler paired with a pressurised unvented cylinder.

Gravity-fed shower pumps (such as twin-impeller brass or plastic pumps in the hot press) must be removed because the hot and cold water supplies are now at direct mains pressure. Existing electric showers that take a cold mains feed can stay in place as an independent backup, while mixer showers are re-piped onto the balanced mains hot and cold feeds.

A straight combi-for-combi swap in the same spot takes one full working day (around 6 to 8 hours). Converting from a traditional system with a hot press copper cylinder and attic tanks to a combi boiler usually takes 1.5 to 2 days, including tank decommissioning, hot press pipework links, system flushing, and commissioning.

Yes. Removing the lagged copper hot water cylinder, immersion wiring, and any shower pump frees up the entire hot press cupboard for slatted shelving and linen storage, while removing the cold water storage tanks in the attic clears floor space overhead.

During the pre-quote survey, the installer measures both static bar pressure and dynamic flow in litres per minute at the kitchen cold tap. If flow drops below 12 L/min at peak times, options include upgrading a restricted internal stopcock, installing a sealed mains accumulator tank, or keeping a system boiler with a rapid-recovery cylinder.

SEAI does not pay a standalone grant for replacing a gas or oil boiler on its own. However, installing a high-efficiency condensing boiler together with zoned heating controls qualifies for the SEAI Heating Controls Grant of 700 EUR on homes built and occupied before 2011.