At a guess you have a 7.6meter pressure reducing valve feeding the cylinder?...and a 3.something relife valve on the roof...you can get a 12 meter head PRV(pressure reducing valve) and whack a 7.6meter relief valve on the roof...This will give you better pressure without the hassle of fully going mains. Not to sure if im 100% correct on this anyone else out there know any better???




Does the origional cylinder have a drain on it as by code....AS/NZS 3500.5 domestic installations....3.22.5 In New Zealand all storage water heaters in excess of 45L capacity shall be provided with a drain pipe valved and capped as appropriate....in saying that your cylinder i assume has a cylinder drain on it which as nessary can be up plugged and branched into to act as a TPR(trempature pressure relife valve) and CWEV(cold water expansion valve)...provided that the drain line is 20mm copper...15mm copper will be too small to allow both valves to work effectivley in case of emergency...In saying that it also depends on where the drain terminates...mate there are alot of possibilities to solving this problem using the codes...does one of the cubboard walls lead to the outside wall...possibility of raising the cylinder and then putting drain inside wall to outside building...also possibility of discharging to tun dish then having a fully glued 88 degree trap then chasing it in to the slab and falling it to the drain or relief gully out side the cwev will keep the trap charged...also raising the cylinder sitting it on a safe tray and discharging to the safe tray with required air gap and chassing in safe tray waste into the slab...
Mate theres alot of ways to solve your problem...the main way to solve your problem is to ring a plumber who has all the revelent codes and standards at his/her fingertips and is able to solve your problem as it dont sound like your standard problem that a home handy man can rip into...but it will cost money! have you had any thoughts of relocating your cylinder to another cupboard in your house to enable this drain line issue not to be an issue?....Good luck I hope this helps cheers

na mate stick with the good old trusty electric cylinder as gas means a line rental and $1500 out lay for the unit and install costs and hassle of paying another bill...any cupboard backing on to a up stairs bathroom will do $300 mains valve kit...run waste out through joist space...easy peasy...lol...hey jax you can tell i dont do gas...push the electric...hahaha