Summary: Learn how to bleed a radiator, repair a pin hole leak in the radiator, repair a leaking pipe joint, repair a leaking valve, repair a leaking bleed valve, repair a leaking radiator gland and repair a leaking drain valve.
If the central heating radiators do not seem to be heating the house efficiently, inspect each radiator to discover which is hot and which is cold. If you find a radiator that is cold at the top but warm elsewhere, this is usually an indication that air is trapped in the upper part of the radiator. To resolve this problem you will need to bleed the radiator using a bleed key.
Hold a cloth under the bleed valve and use the bleed key to open up the valve, without removing it completely.
A pinhole leak producing a small jet of water is caused by corrosion inside the radiator. Although pouring a plastic resin sealant into the feed-and-expansion tank can achieve a temporary repair, this is usually only a short-term measure. You must not use this type of sealant in a sealed central heating system. For this type of system you will need to replace the radiator.
Modern central heating systems mainly use compression valves to join pipes to the radiator. If one of these joins is leaking you may be able to remedy it by tightening the valve with a spanner by a quarter of a turn. However, if this fails to stop the leak you will need to perform the following procedure:
Starting at the end of the male thread of the valve tail, tightly wrap it with PTFE tape.
A leaking bleed valve or air vent is easily repaired.
If water is leaking from under the plastic cap, the packing gland needs replacing. This can be done using PTFE tape.
Stretch a length of PTFE tape into a string, then wrap it around the spindle four or five times.
If the drain valve is leaking, its washer probably needs replacing but you will need to drain the system to repair it.
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