Boiler Installations in London and Kent

When a new boiler is the answer

Plenty of boilers that stop are worth repairing, and the repairs page is where that conversation starts.

A replacement starts to make sense when the parts for the model are no longer made, when the same boiler has failed three or four times in a couple of winters, when the heat exchanger itself is leaking or corroded, or when the house has changed round it, a loft conversion or an extra bathroom, and the old boiler no longer keeps up. Age on its own is not a reason. Plenty of older boilers run well because somebody looked after them.

• Boiler Repairs in London and Kent

Combi, system or regular

Three kinds of gas boiler cover nearly every house we work in.

A combi heats water as you use it, straight off the mains, so there is no hot water cylinder and no tank in the loft. It suits a flat, or a house with one bathroom where two showers rarely run at once. A system boiler runs the heating and keeps a cylinder of stored hot water hot, on a sealed, pressurised system with nothing in the loft. A regular boiler, sometimes called heat only, is the older arrangement: a cylinder, a cold water tank in the loft and a small expansion tank beside it. Which one is right is decided by the house rather than the brochure: how many bathrooms there are, how many people shower at the same time, what the incoming water supply can deliver, and where there is room to put things.

• Whether the water supply will carry a combi, on the Belvedere page

Sizing it for the house

A boiler is sized twice. Once for the heating, by how much heat the house loses on a cold day, and once for the hot water, which on a combi comes down to how many litres a minute it can deliver to a tap or a shower. Bigger is not better. The building regulations say a heating system should not be significantly oversized, and a boiler that is too big for the house tends to switch on and off in short bursts instead of running steadily. The next edition of those regulations, which takes effect in March 2027, goes further: it says a replacement should be sized from a heat loss calculation for the whole house, and not copied from the output of the boiler coming off the wall.

That is a sensible way to work whatever the date.

The day it goes in

Most of a boiler installation is the work around the boiler. The old unit is isolated, drained down and taken off the wall, and the system is flushed before the new one is connected, so years of sludge from the old radiators do not go straight into a new heat exchanger. A filter goes on the return to catch what the flush misses. The gas supply is checked against what the new boiler needs at full output, because a pipe that was big enough for the old boiler can be too small for the new one, which is the subject of one of the jobs written up below. The flue is fitted to the manufacturer’s instructions, through the wall or up through the roof, and the condensate pipe is run to a drain with a fall that will not hold water. Then the controls go on, the system is filled, bled and pressurised, and the boiler is commissioned: lit, checked and set up for the house it is in, rather than left on the settings it came out of the box with. Before anyone leaves, you are shown how it works, where the filling loop is, what the gauge should read and what to do if the display shows a fault.

The gas, the flue and the flush are the job as much as the boiler is.

• New boiler flue through the wall
• New boiler gas pipe size
• Combi boiler installation on a bare wall

Controls that come with it

A replacement gas boiler in England has to meet the building regulations, and they cover the controls as well as the boiler. The boiler must reach at least 92% seasonal efficiency. It needs time control, temperature control and an interlock, so it does not fire when nothing is asking for heat. When a boiler is replaced, each room should also have its own thermostatic control, usually a radiator valve, unless there is a sound reason not to. A combi needs one more energy measure from a short list: weather compensation, load compensation, a smart thermostat with automation and optimisation, or flue gas heat recovery.

Which of those suits the house is explained at the visit.

Moving a boiler, and back boilers

Moving a boiler to another wall, a cupboard or the loft is a bigger job than a straight swap, because the gas, the water, the flue and the condensate all move with it, and the new spot has to let the flue out and leave room to service the boiler afterwards. An old back boiler behind a fire in the chimney breast is the biggest change of all. It usually means a new boiler somewhere else in the house, the old one taken out, the chimney made safe and the hot water arrangement rethought from the start.

• Back boilers in the chimney breast, on the Penge page
• Where a flue is allowed to come out, on the Swanley page

The quote, in writing

Every installation is quoted after somebody has been to the house and looked, because the right boiler, and the right price, depend on things nobody can see from a phone call. The quote says which boiler, where it goes, the flush and the filter, the gas and flue work, the controls, what happens to the old one, and anything else the house needs, so there is nothing to find out on the day.

Nothing is fitted on a guess.