While all Gas Safe registered installers are familiar with the dangers of Carbon Monoxide (CO), a concealed flue can present a real challenge.

A fully-sealed flue system is essential to carry the poisonous gas away to safety - but if you can't see the flue, you can't be sure there are no leaks. Industry guidance states that any boiler with a hidden flue should be classified 'at risk' and should be temporarily disabled. To get the boiler back up and running again, you then have two options:

Inspection hatches

Installing inspection hatches for boxed-in flues allows you to see along the full length of the flue. But while this can be a great solution, it can have complications.

Firstly, a building professional will have to be hired to carry out the installation work, and if this takes time to sort out, the house will be left without heating and hot water.

It's also possible that the householder could be against the installation of the hatches - as they can be seen as costly, disruptive or unattractive.

Void monitoring safety shut-off

The simpler alternative to installation hatches is a void monitoring safety shut-off system. Even though the flue remains hidden in this case, the system provides protection for the householder by automatically shutting down the boiler if CO is detected.

The system works by using CO sensors, connected wirelessly to the control unit. If any of the sensors detect CO, a signal is sent to the control unit, which in turn cuts the power supply to the boiler.

An audible alarm would also sound to alert the occupants of the house.

Find out more about NoCO, the carbon monoxide detection and gas shut off system.