What is this fitting please?

[Richard Frost]

Hi, I'm hoping someone can help, I have this fitting on what I think us the overflow pipe from my hot water tank. I have noticed a damp patch on the ceiling below it and it seems that when there is water passing along the pipe it overtops the 'cup' and overflows. If the image is not visible it is a black fitting, positioned vertically with an open 'cup' on the bottom half.
I assume that the pipe only runs water when the HW gets to a certain temp (although this us pure guesswork tbh) I have recently had a PV system installed and hence the immersion heater is used these days, whereas it was never switched on before.
I cannot see the point in this fitting and I was thinking about just taking it out and piping straight through the gap. There is an overflow to outside.
Could someone explain it please
Many thanks
Richard

Edit - sorry, I cannot seem to get the image to upload, but the link is here Dropbox - File 07-05-2017, 22 38 58.jpeg

 

[ShaunCorbs]

It's a tundish and if it's running there's a problem

Best get it look / serviced by an unvented reg tech (G3)

 

[Best]

Do not touch it! It must be a tundish by your description and is there for a purpose. Get a G3 qualified plumber (qualified in unvented hot water systems) to look at it.
Shaun beat me to it.

 

[Harvest Fields]

As above. You need a specific certificate to work on the cylinder that you have. Best to get a pro in.

 

[Callsimon55]

This is a tundish through which water passes when the safety pressure valves operate on hot water cylinder or sealed heating system. You have a problem!

 

[townfanjon]

Richard I think you realise by now you have a problem , do not remove the tundish , if it helps you could ask on here for a G3 engineer.