Position of cylinder vent

[petey]

Hi folks - I'm a newbie to this forum, so please be gentle!
The boiler is an old but trusty Trianco oil-fired job, sited on the ground floor of a single storey extension - pump, motorised valve & cylinder are mounted above in Y plan format. I've just updated these with a Danfoss FP715SI controller.
Distribution to the rads passes up/down/everywhere thro stone wall into the main part of the house.
In general the nightmare of pipework seems to deliver the heat to the right places, but it all needs to be tidied up - which is underway.
One of these pipes is a 15mm vent from the top of cylinder that eventually makes its way to the CW cistern, with many twists and turns.
My question is - is it possible to replace this with a T into a 22mm feed to a remote bathroom that runs direct from top of the cylinder, thro the wall & below the cistern? The T would be about 1m below the cistern water level.
cheers

 

[kirkgas]

Hi folks - I'm a newbie to this forum, so please be gentle!
The boiler is an old but trusty Trianco oil-fired job, sited on the ground floor of a single storey extension - pump, motorised valve & cylinder are mounted above in Y plan format. I've just updated these with a Danfoss FP715SI controller.
Distribution to the rads passes up/down/everywhere thro stone wall into the main part of the house.
In general the nightmare of pipework seems to deliver the heat to the right places, but it all needs to be tidied up - which is underway.
One of these pipes is a 15mm vent from the top of cylinder that eventually makes its way to the CW cistern, with many twists and turns.
My question is - is it possible to replace this with a T into a 22mm feed to a remote bathroom that runs direct from top of the cylinder, thro the wall & below the cistern? The T would be about 1m below the cistern water level.
cheers

a 15mm vent is a no-no under any circumstances so if you are unsure it is best to get a real plumber in as soon as possible to sort this out for you

 

[petey]

kirkgas - thanks for your input. I am aware that the norm for the vent is 22mm, but this arrangement has been in place since at least 1985, with no change to the boiler/cylinder/pipework. So it may be a no-no, but it works, though I do appreciate the sentiment behind your comment.
The question is - what is the significance of the sizing - is it to do with the relative size of the column of water expanding and flowing over?
Because the loon who installed this arrangement built this expansion pipe into a stud wall, I'm reluctant to rip it apart until I'm sure it's really worth it. My dilemma is that this is just one of the examples of lousy pipe work, which I'm in the process of replacing/rerouting.
That notwithstanding, what of my query about moving the vent origin? Is this a goer? I might be then able to route a 22mm pipe up and over the cistern. So this will serve the expansion function, but what of the air?
cheers