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How to fix leaks in a central heating system

Skill Level: Intermediate


 Leaks in a central heating system can be a nightmare! Once discovered they should not be ignored. Fresh water that is drawn into a system to replace water that is lost due to a leak contains free oxygen which causes radiators and some boilers to rust.

Internal leak sealants similar to those used to fix leaking car radiators can be used for repairing minor leaks in central heating systems. In this method the sealant is poured directly into the feed and expansion tank. If this fixes the problem…you may have just escaped lightly.


Leaking pipe joints

Very often, leaking pipes originate from compression joints which can be quite easily fixed by simply tightening with an adjustable spanner or wrench. But be careful to tighten the fitting only slightly, if this does stop the leak after a quarter of a turn - don’t go any further or you risk damaging the joint.
Where tightening the joint does not solve the problem then you will either have to;
Drain the system to below the leak, or, isolate the area by closing valves either side of the leak. Once isolated, loosen off the joint fitting and reseal the threads with PTFE tape, and then tighten up.

Leaking radiator valves

If the leak is from the compression joint below the valve, then drain down the system and turn off the valves at both ends of the radiator. Count the number of turns on the lockshield valve and make note of the number.

Use rags and a bowl to catch water

Make sure you put rags and a bowl under the valve as you are working to catch water. Better still, have a second one close by, just in case.

Tools for the job

There’s not a lot in the way of tools required. Take an adjustable spanner or wrench and turn the union nut anti-clockwise, when looking from the radiator to the valve. Careful here, some water may run out.

PTFE sealing tape

Wind a length of plumbers PTFE tape around the male thread on the valve. Begin at the end and overlap the tape as you wind on.

Replace the nut and re-open valve

Finally, replace the nut and open the valves and air vent. Now, open the lockshield valve by the same number of turns that were required to close it.
Once done, check for leaks and close the air vent when water starts to appear.

Leaking tail valves

It may be the leak originates from the valve tail which is screwed into the radiator. This may be undone by using an Allen key or a large screwdriver. Again, once loosened off, cover the thread with PTFE tape, and re-connect.

Leaking radiator vent

Occasionally, leaks originate from the radiator air vent. If this is the case, then again, drain till below the height if the air vent, unscrew, and cover the thread with PTFE tape – tighten up and switch the water back on.

Tools you will need:
Rolson 350mm Stillson Type Pipe Wrench
Rolson 350mm Stillson Type Pipe Wrench
- P.T.F.E. Tape 12mm x 12m - Twin Pack
P.T.F.E. Tape 12mm x 12m - Twin Pack
- Britool 7pc Torx Hex Key Set T10-T40
Britool 7pc Torx Hex Key Set T10-T40
- Bahco (80 Series) 100mm Chrome Adjustable Wrench
Bahco (80 Series) 100mm Chrome Adjustable Wrench

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