This is leaking

[SJRSJR]

Have discovered there is a slow drip from this tap (photo taken from above) on my central heating pipes under the floorboards. It explains why the water pressure in the boiler drops periodically. Is it a drain valve and can I try and tighten the square nut or will it need replacing? Thanks

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[Hugh Jaleak]

You can try pinching up the square key end to tighten the valve slightly more, but I suspect you'll be better off replacing the washer. Unscrew the guts of the valve, (will need to drain system or work quickly to avoid loosing too much water), replace washer and refit.

 

[SJRSJR]

Thanks. Have tried tightening it but it seems immovable. Don't want to use too much force for fear of call out charge on a Bank Holiday!

 

[Hugh Jaleak]

In that case maybe best to change the entire valve. http://www.screwfix.com/p/drain-cock-type-a-heavy-pattern/96725 Use PTFE on the thread to seal the joint.

Recommend you use a second wrench to support the T piece to avoid twisting the pipe when undoing the existing fitting!

 

[SJRSJR]

Thank you, that's very helpful.