Chimney check for a gas boiler

When a gas boiler flue needs a certificate

• Boiler replacement: when a heating appliance is replaced with another, the flue and ventilation are checked, and before the new appliance is used the certificate records whether it may be connected to the flue.
• Gaso's simplified procedure: one of the conditions is connection to the existing flue channel with a certificate on the technical condition of the flue channel and ventilation ducts.
• The boiler has been disconnected for more than six months: an extraordinary check of the flue gas exhaust and ventilation ducts with a certificate is needed.
• Regular maintenance: a gas appliance is cleaned, serviced and checked once a year unless the manufacturer specifies otherwise.
• Centralised flue gas exhaust, for example a shared flue in an apartment building: the natural gas regulations require the condition and connection of the flues to be confirmed by a technical condition inspection certificate.

Gaso's simplified replacement procedure and the flue certificate

Gaso's simplified procedure applies to users with consumption up to 16 m³/h and appliance output up to 130 kW, if the new appliance is installed in the same room. The documents are submitted to Gaso's regional office, and one of them is a certificate on the technical condition of the flue channel and ventilation ducts.

The boiler is replaced by an installer with a gas appliance certificate, and Gaso refers to a register of such specialists. Our part is the flue and ventilation: we check whether the existing flue channel suits the new boiler and draw up the certificate. It is better to do this before buying the new boiler, because then you can still choose a boiler that suits the existing flue, or plan a liner in good time.

What we check in a gas boiler flue

1. Boiler and flue We note the boiler type (open-flue, room-sealed or condensing) and the flue material: brick, liner, ceramic or metal.
2. Cross-section We measure the flue channel. The building code requires at least 50 cm² or an 80 mm diameter for gas appliances. For a more powerful boiler the required size is set by the manufacturer's instructions.
3. Shared flue We check that no stove or fireplace is connected to the same flue channel. The building code prohibits it.
4. Inside When inspecting the inside (for example with a camera), we look for crumbled joints, traces of condensation, displaced liner sections and blockages.
5. Ventilation We check the draught of the boiler room's ventilation duct and that flue gases are not discharged into a ventilation duct.
6. Certificate We fill in the Annex 8 form and record in the remarks whether the boiler may be connected to the flue, with photos or video.

A condensing boiler and an old brick chimney

The flue gases of a modern condensing boiler are cool and moist. In an old brick flue they cool down, the moisture condenses on the walls, and the acidic condensate gradually dissolves the mortar. That is why such a boiler usually needs a liner made of a material the manufacturer intends for condensate. If the inspection shows the existing flue does not suit the new boiler, this is recorded in the certificate, and the solution is usually a liner: liner for a gas boiler. On signs of moisture: condensation in the chimney.

How often a gas boiler flue must be checked

The boiler itself must be serviced once a year whatever the flue material. The full table by fuel: how often to clean a chimney.

How much does a chimney check for a gas boiler cost?

There is no fixed price for this inspection. It depends on the number of flues and ventilation ducts, the length and diameter of the flue, access to the roof, whether a camera is needed and whether the flue must be cleaned. In an apartment building with a shared flue the job is bigger than in a private house. The specialist will name the price after you submit the form, before the work. Other jobs: prices.