no vent pipe?

[mah]

here goes. i was workin with my old boss today whos a meber of the iphe so knows what hes doing, went to a y plan three port system that was being supplid by a 22mm cold feed from the expansion pipe on the return,yet no open vent. the pump is on the return the three port is on flow,and on the return tapping of the hot water cylinder. also theres reverse circulation due to wrongly teed in.theres little height for a vent from the flow to stop pumping over,he said you could get away with no vent as altering the system could be a complete rip out and start afresh and put a prv and a aav would help. would this be correct im only an apprentice and a bit confused any help would be appreciated if this would be ok

 

[ollski]

No problem with a combined feed and vent as long as it's in 22mm.

 

[mah]

so thats what a combined vent and feed is thanks i thought it was when the vent pipe branches of the feed. is it worth putting a prv in then

 

[mah]

also ollski the boiler was a grandee oil boiler wich i noticed was at least about 1-2 m above the tank yet working on a one pipe system without a tiger loop. its been workin about 4-5 months without any problems. how i thought an oil boiler cant work this way