Get it Right,
You have a bigger issue here… You may want to do some research on the OH&S requirements re pressure vessels.
We had gravity feed hot water tanks in the ceiling, being the original hot water tanks in the building. On behalf of our OC I investigated our options at length, searching for the most cost effective, and possibly energy efficient option (see Jimmy tomorrow at the Green Forum), as the hot water tanks are common property in our building. So I looked into solar, gas boosted solar or just plain gas, together with the concept of placing mains pressure electric tanks inside the laundry of each apartment or otherwise mains pressure electric tanks in the ceiling, or gravity feed in the roof again. Any plumber I spoke to about the mains pressure in the roof clearly stated this should not even be considered unless you are ok with having a bomb in the roof. It is an extremely risky situation as they are a bit of the out of site, out of mind, so no one will keep an eye on them until something goes wrong… And when if that happens it could be seriously disasterous.
Interestingly, we ended up replacing the 8 gravity feed tanks with a reticulating gas hot water system. The other owners did not wish to go with the cheapest option (after the government rebate) being the gas boosted solar system. Also, though we were replacing 8 tanks with just 2, when I investigated government rebates (at the time) we were only eligible for 1 rebate instead of 8…
In long and short, the owner’s have done the wrong thing and should agree to correcting this, and paying all costs associated, or if not be prepared to remove the hot water tank from the ceiling space. There are two sections of the act that are relevant, being s52 and s65a.