Hot water filter? Pressure relief valve

[AndyPRK]

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I have this system in my house.

I intend to change the stop cock because it doesn't work.

Out of interest could someone explain what the 2 items are and do please.

I ask for 2 or 3 reasons.

1. Previously when I have turned the water off at the mains to perform work on the hot water taps, the water is off and then suddenly there will be a significant amount of water comes out and makes a mess, and then stops. I assume that white cylinder is causing this ? Even if I replace that stop cock and use it, it will still have the same result. How do plumbers work round this?

2. I do get a drop of water out of the external pressure relief pipe. This can come from 2 sources. That bar thing out the back, and a pressure relief valve ontop of the cylinder. (I actually think it's coming out of the cylinder one)

3. At some point I will need to get a qualified (unvented) plumber to replace that thing with the limescale on. I have previously been told it's a filter? Seams to have too many pipes though? So that I can purchase one to have on hand, what am I looking for?

 

[McCombi]

Send the pics to whoever is going to do job and they will keep you right. Needs someone with unvented hot water qualification

 

[AndyPRK]

just done a bit of a search

So it's a pressure reducing valve and strainer.
With a cold water output to match the pressure of the hot (I guess this does the shower/bath)

Maybe a non return valve in their somewhere.

Then the expansion vessell for when the water heats up.
and expansion valve blow off.

Have to have a read.

 

[dilalio]

Have to have a read.

And then call a G3.