System and regular boiler service in London

A regular boiler, also called a heat only or conventional boiler, works with a hot water cylinder and usually two tanks in the loft. One tank feeds cold water to the cylinder and one small tank tops up the heating. This is common in older and larger London houses.

A system boiler has the pump and expansion vessel built in, so it does not need the small heating tank in the loft. It still heats a cylinder. Many system boilers in London houses are paired with an unvented cylinder, a sealed tank fed straight from the mains that gives stronger hot water pressure.

Both types are more common in the outer suburbs we cover, such as Bromley, south Croydon, Wimbledon and Ealing, where family houses have airing cupboards and lofts. Converted flats in inner south London are mostly combis.

Because hot water is stored, the controls between the boiler and cylinder matter. A sticking motorised valve can mean hot water but no heating, or the other way round. A failing cylinder thermostat can leave water too cool or too hot.

Unvented cylinders hold water under mains pressure. They have safety devices: a pressure relief valve, a temperature and pressure relief valve and an expansion vessel. Makers ask for these to be checked regularly, usually yearly, by someone competent in unvented hot water systems. Ask for it when you book so the right checks are planned in.

In London's hard water, scale builds up in cylinders too, especially around the coil that the boiler heats. A slow cylinder that takes much longer to heat can be a sign.

Open vented systems, the ones with a loft tank, take in a little fresh water and air over the years. That leads to rust inside radiators, which settles as black sludge. You see radiators that are cold at the bottom and warm at the top.

A magnetic filter on the return pipe to the boiler catches much of it. If you do not have one, or yours has not been cleaned, the engineer can talk you through our magnetic filter clean and system health check.

Gas work in the UK must be done by a Gas Safe registered engineer. Ask to see the ID card and check it on the Gas Safe Register.

Regular boilers in older London houses are sometimes in the loft, the kitchen, or even the basement of a split level house. A loft boiler needs a safe ladder, boarding to stand on and a working light so the engineer can take the case off. Tell us where yours is when you book.

The airing cupboard also needs to be reachable. Clear shelves around the cylinder thermostat and valves before the visit if you can. On unvented cylinders, the discharge pipe from the safety valves (called a tundish and pipe) should be visible and run to a safe place outside. The engineer will check it is clear.