System boiler installationin Milton Keynes

The giveaway is what is missing. There are no tanks sitting in the roof, because the heating side runs sealed and under pressure, topped up from the mains through a filling loop. The vessel that takes up the slack when heated water expands is built into the boiler, and so is the pump that pushes water round the radiators.

Hot water still comes from a cylinder, normally in an airing cupboard. The boiler heats a batch of it and the insulation holds the temperature until somebody wants a bath. That is the real difference from a combi: you are drawing on water that has already been heated instead of asking one appliance to heat it as it runs.

Plenty of Milton Keynes houses built between the 1970s and the 1990s started life with a cylinder on the landing and a pair of tanks above it. Moving that setup onto a sealed system is one of the most common upgrades on this housing stock, and it gives you the loft back.

That is why people like them. Showers feel strong without a pump, hot and cold arrive balanced at a mixer tap, and a converted loft stays a loft. The catch is that it only works if the incoming main can deliver, so the installer tests pressure and flow before recommending one.

Because water is being stored hot and under mains pressure, an unvented cylinder carries safety devices and a discharge pipe that takes any release safely outside. At the storage sizes used for domestic hot water, fitting one is notifiable building work under the Building Regulations, and it must be installed by an installer qualified for unvented hot water systems. An installer registered with a competent person scheme for that work self certifies it. Anyone not registered has to notify building control before the cylinder goes in.

Ask for the installation and commissioning record, usually the Benchmark document, and keep it with the boiler paperwork. The safety devices are checked as part of the annual visit, so put the cylinder on the same appointment as the boiler when you bookboiler servicing.

1. The system is drained and the water and gas isolated.
2. Old boiler off the wall. On a conversion, the loft tanks and any redundant pipework come out.
3. Heating circuit sealed and a filling loop fitted, with pipework altered where the new unit sits.
4. Cylinder connected, or a new one fitted and its safety devices and discharge pipe set up.
5. Boiler hung, flue fitted and the condensate routed to a drain.
6. System flushed, inhibitor added and a filter fitted before anything is brought up to temperature.
7. Boiler and cylinder commissioned, controls set, paperwork completed and handed over.

A straight system for system swap is usually a day. Allow two where the loft is being cleared and a new cylinder is going in.