Combi Boiler Installation and Replacement

When a combi suits a Borders home

A combi does two jobs from one box: it heats the radiators and it heats water on demand, with no hot-water cylinder and no cold-water tank in the loft. That frees up a cupboard and removes the wait for a cylinder to reheat. The trade-off is that hot water performance depends entirely on the water coming into the house.

On many rural Borders supplies the pressure is fine but the flow rate is modest, especially at the end of a long supply pipe or on a private supply. A combi can only deliver what the main gives it, so we test the flow with a gauge rather than guess. If two showers are likely to run together, a system boiler with a cylinder is usually the better choice, and we say so.

• Good fit: one bathroom, perhaps a separate shower room used at different times
• Good fit: flats and smaller houses where cupboard space matters
• Think twice: two or more bathrooms in regular simultaneous use
• Think twice: low incoming flow that would leave showers weak

Switching from a system or regular boiler to a combi

Many older homes still have a regular boiler with a hot-water cylinder in an airing cupboard and tanks in the loft. Converting to a combi means removing the cylinder and the tanks, capping redundant pipework and re-routing the hot and cold feeds so the taps are supplied straight from the combi and the main. It is a bigger job than a like-for-like swap, but it often frees a whole cupboard and removes a loft tank that could freeze or leak.

Before agreeing a conversion we check that existing showers and taps will work on mains pressure. Older gravity-fed shower valves and some mixers are not designed for it and may need changing, which we include in the written quote rather than discovering on the day.

Sizing, flue position and controls

Combi size is set by hot water demand more than by the size of the house, because heating water instantly takes more power than heating radiators. A larger combi will not fix a poor supply, though: if the main cannot deliver more water, extra output is wasted. Our guide on what size boiler you need explains the reasoning in more detail.

The flue has to meet clearance rules from windows, doors and boundaries, and a new boiler position can mean a new route for the condensate pipe. We plan both on the survey and fit the condensate run to reduce the risk of freezing in a hard winter. We also fit sensible controls, such as a programmable or smart thermostat, so the new boiler runs efficiently from the start.

Gas, LPG and oil combis

Most combis we fit run on mains gas, and LPG versions are available for homes off the gas grid. Oil combis exist too, and can suit an off-gas property with modest hot water demand. Graham installs all makes, with Vaillant as his preferred manufacturer as an approved Vaillant Advanced Installer. If you are comparing types first, our combi vs system boiler guide sets out the differences in plain terms.

We cover Kelso, the Scottish Borders and East Lothian.