Identify this part

[Pmach]

Can anyone identify what the part in the picture is. I've worked out that the square box behind it is a one way valve for the CH flow.
This part pictured is on the flow to the heat exchanger in the HW cylinder.

 

[cross thread]

Pressure relief valve

 

[Pmach]

Is it necessary for an open vented system with an F+E tank to have a pressure relief valve?

 

[fixitflav]

Is it necessary for an open vented system with an F+E tank to have a pressure relief valve?

AFAIK, no

 

[ianmcd]

Is it necessary for an open vented system with an F+E tank to have a pressure relief valve?

Was your system solid fuel fired at one time, they used to be fitted with coal back boilers

 

[Pmach]

Was your system solid fuel fired at one time, they used to be fitted with coal back boilers

I'm not sure, it's currently oil fired, those pipes are in a back porch/boiler house. It all looks like a DIY job to be honest, an ok one though, seems to have been going for many years.

 

[Exedon]

That set up was almost standard practice 40 odd years ago.
Spring loaded safely valve and some sort of non return valve to stop gravity circulation.
The square thing is probably made by smc.

 

[gas112]

if its not leaking and sealed its self just leave it . Lost count of the amount of these that we snatched 20 seconds as opposed to messing about draining down