Boiler installation

When this is the job you need

Boiler installation, as opposed to a straight replacement, usually means one of four situations:

• a property with no wet central heating at all — often electric heating or a solid fuel system — having a boiler and radiators fitted for the first time;
• moving a boiler from where it is now to somewhere more useful, typically out of a kitchen cupboard or into a utility room or loft;
• changing between boiler types, for example removing a cylinder and loft tanks and moving to a combi;
• a conversion, extension or renovation where the heating system is being reconfigured anyway.

If the boiler is staying broadly where it is and doing the same job, that is a boiler replacement, which is a shorter and less involved piece of work.

Where a boiler can actually go

Siting is decided by physics and regulation rather than preference. Four things have to work at once:

• The flue. Combustion gases have to discharge safely, which means minimum distances from openable windows, doors, air bricks and boundaries. Flue routes through voids need to remain inspectable.
• The condensate drain. A modern condensing boiler produces acidic condensate that needs a fall to a suitable drain. Where that involves an external run, it must be protected against freezing — frozen condensate is one of the most common winter callouts.
• Gas supply. The existing supply pipe has to deliver enough gas at the right pressure for the appliance. On longer runs or higher-output boilers, an upgrade is sometimes needed.
• Access. The boiler needs clearances around it for servicing and repair. A boiler sealed into a tight enclosure creates problems for every engineer who comes after.

Sizing the boiler correctly

Oversizing is the most common fault in domestic boiler installation. A boiler far larger than the property needs will cycle on and off rather than running steadily, which wastes fuel and wears the appliance.

Output should follow from the property's heat loss and, for a combi, from the hot water flow rate the household actually needs. If a quotation names a boiler output without any reference to the size of the property or the number of bathrooms, ask how it was arrived at.

The system around the boiler

A new appliance connected to a dirty system will not perform, and will not stay under warranty for long. A proper installation therefore includes:

• a thorough system clean, usually a chemical flush appropriate to the system's condition;
• a magnetic filter on the return, to capture debris before it reaches the boiler;
• inhibitor dosed into the system water to slow corrosion;
• checking radiator valves and, where relevant, balancing the system afterwards.

Controls are worth attention at the same time. A programmable room thermostat and thermostatic radiator valves make more difference to comfort and running cost than the choice between two similar boilers.

Notification, certificates and paperwork

Installing a heating appliance is notifiable work under the building regulations. It is normally handled by the installer through a competent person scheme, and you should receive:

• a building regulations compliance certificate;
• the commissioning record for the appliance;
• the manufacturer's warranty registration;
• the user and service documentation for the boiler.

Keep all of it. These documents are asked for when you sell the property, and a missing compliance certificate is a slow and irritating thing to resolve years later.

Commissioning and handover

Commissioning is where the installation is set up to run properly: checking gas pressure and rate, setting the flow temperature, adjusting the controls, balancing radiators and confirming the flue and condensate arrangements. A rushed handover is the point at which an otherwise good installation starts underperforming.

Ask to be shown how the controls work rather than being handed a manual. Five minutes at that stage saves a winter of guesswork.

Before you commit: is a boiler definitely the answer?

If you are installing a heating system from scratch, or reconfiguring one substantially, it is a natural moment to compare a boiler against a heat pump — particularly if the property is off the mains gas grid. Much of the work is common to both, and grant support may apply to one of them and not the other.

That comparison is set out in our guide to heat pumps and gas boilers, and the grant position on the Boiler Upgrade Scheme page. There is no scheme funding for a conventional gas boiler.