Slow dripping L connection under sink

[Old UKPF 98003]

Hi,

I have a leak under the sink and have found the source, that being a L shape pipe connection which is behind some plaster board.
To the right of the sink there is a dishwasher and to the left there is a washing machine.
The damp plasterboard is due to my genius idea of putting a rag around the leak last night which transferred the water to the paster board. I am currently doing my best to capture the water that drips with a tray and rags underneath.
A few questions I have are, what is the pipe? I assume it connects to the dishwasher however it still slowly drips even though the dishwasher has not been on for a couple of days.
How can I stop the dripping for now? From the photo you can see I have a water tap and on the left of the photo there is a blue lever too.
How much would it cost to fix the leak? Assuming it is just the L connector.

Thank you.

 

[ShaunCorbs]

I would say it's from your boiler if it's close

 

[Old UKPF 98003]

I would say it's from your boiler if it's close

Hi, thanks for replying. The boiler is in the bedroom which is directly above the kitchen.

 

[ShaunCorbs]

Could be from that tbh best option is to get a plumber out to replace the elbow and damaged part of the pipe

 

[Old UKPF 98003]

I feel that is best. Do you have a general idea of the cost to fix the issue if it is just the elbow?

 

[ShaunCorbs]

At a guess under £200 but that's just a guess

 

[Old UKPF 98003]

At a guess under £200 but that's just a guess

Thank you, its good to have an idea. Arranging for a plumber now. Thanks again.