Guide
Converting to a combi boiler
Most older Irish homes have a boiler, a hot water cylinder in the hot press and a cold water tank in the attic. Converting to a combi takes the cylinder and tank out and heats water straight from the mains.
What changes
- The hot water cylinder and immersion come out of the hot press. You get the space back.
- The cold water storage tank comes out of the attic, along with its pipework.
- Hot water comes at mains pressure, straight from the boiler, whenever you open a tap.
- The gas pipe may need upgrading, because a combi burns more gas at full output than a heat-only boiler.
When it's a good idea
One bathroom, decent mains pressure, and a household that rarely runs two showers at once. You stop heating a full cylinder you don't use, and the boiler only fires when you need hot water.
When it isn't
Two or more bathrooms in daily use at the same time, or weak mains pressure. A combi splits its flow between outlets, so both showers lose out. A system boiler with an unvented cylinder may suit better. Also think about heat pumps: if one is likely in your future, the cylinder you'd need is the one you'd be removing.
What it costs
Published conversion prices run from €3,100 to €4,000, median €3,400, across 3 installers. It costs more than a like-for-like swap because the cylinder and tank come out and the hot water pipes change.
| Installer | County | Job | Price | VAT | Source |
|---|---|---|---|---|---|
| Dublin Plumbing & Gas | Dublin | Gravity-fed (tank + cylinder) system to combi conversion (range) | €3,100–€3,850 | incl. VAT | site |
| Gasworks (Gas Works Engineering Ireland Ltd) | National | System to combi conversion (apartment) | from €3,400 | not stated | site |
| Gasworks (Gas Works Engineering Ireland Ltd) | National | System to combi conversion | €3,500–€4,800 | not stated | site |
| Gasworks (Gas Works Engineering Ireland Ltd) | National | System to combi conversion (3-bed home) | from €3,800 | not stated | site |
| Gasworks (Gas Works Engineering Ireland Ltd) | National | Regular boiler + hot water cylinder to combi conversion - existing boi | €3,995 | incl. VAT | site |
| Gasworks (Gas Works Engineering Ireland Ltd) | National | System to combi conversion (regular boiler + hot water cylinder to com | €3,995 | not stated | site |
| Dublin Gas Boiler Service | Dublin | Back boiler to combi conversion (typical range) | €4,000–€6,500 | not stated | site |
| Gasworks (Gas Works Engineering Ireland Ltd) | National | Regular boiler + hot water cylinder to combi conversion - new boiler l | €4,495 | incl. VAT | site |
| Gasworks (Gas Works Engineering Ireland Ltd) | National | System to combi conversion (regular boiler + hot water cylinder to com | €4,495 | not stated | site |
| Gasworks (Gas Works Engineering Ireland Ltd) | National | System to combi conversion (boiler relocated to attic) | from €4,800 | not stated | site |
Extras that often come with a conversion
| Extra | Published price | Who publishes it | Source |
|---|---|---|---|
| Power flush, 3–4 bed house | from €950 incl. VAT | Freeman Plumbing, Naas | site |
| Moving the boiler on a combi conversion | +€500 (€3,995 same spot, €4,495 new spot) | Gasworks | site |
| Mains water booster pump | +€600 | Gasworks | site |
A booster pump is only needed where the mains pressure or flow is too weak for a combi. Ask the installer to test it before quoting.
Questions people ask
How much does it cost to convert to a combi boiler?
Published conversion prices run from €3,100 to €4,000, median €3,400, across 3 installers. It costs more than a like-for-like swap because the cylinder and tank come out and the hot water pipes change.
Will my shower work with a combi?
Electric showers are unaffected. A shower fed by a pump from the hot press usually changes to a mains-pressure mixer shower, because the combi supplies hot water at mains pressure. Your installer should check this before quoting.
What happens to the immersion?
It goes, along with the cylinder. If the boiler breaks down you have no backup hot water, so an electric shower is handy to keep.
Is there a grant to convert to a combi?
No. In SEAI's own words, it "does not provide grants for the installation of new or replacement fossil fuel boilers, such as gas or oil boilers" (SEAI). You may get the €700 heating controls grant if your home was built and occupied before 2011 (SEAI). The €2,000 boiler scrappage grant only applies when a heat pump replaces the boiler.