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In the months after a system has been filled and periodically during the life of a system air bubbles can form in the water in the radiators. This will collect in the highest part of the radiators. Large amounts of air collecting in one radiator will cause the top to remain cold even when the rest of it is hot.

The aim of this task is to open the bleed valve at the top of the radiator that allows the air to escape. It is best to do this when the system is hot and at higher pressure. This may result in the system pressure becoming too low and needing to be topped up.

WARNING: Do not open the valve too far as there is a risk the centre pin will come out. An excessive amount of water would be lost from your system causing water damage to the building around the radiator.


Sometimes air can build up in a section of pipework and prevents water getting to one or more radiators. This is usually solved by turning off all the radiators that are working and then forcing the air into a radiator from which it is bled. To do this:

1. Turn off all the radiators except the one that isn’t working. (Set the TRVs to ‘0’)
2. Force the system to run by turning up the thermostat and making sure the timer is on a ‘heating on’ period or set to ‘continuous’.
3. After a short time the radiator should become hot.
4. Follow the procedure for bleeding the radiator.



If you smell gas, turn off the boiler. Turn off the gas supply at the gas station. Call us on 0800 693 876. Do not remove, block or cover the flue. This could lead to dangerous fumes being released inside the home.


The general aim is to add mains water to the existing water in the central heating system. This is done by connecting a mains water supply, using a garden hose, to the system drain and fill tap. This should only be done when the system is cold.