It’s amazing how many of these Simplex hot water cylinders we come across in the Auckland area. This year we ripped out more than 100 Simplex hot water cylinders! In most cases the hot water system was converted to a main pressure system which required an installation of an additional drain and mains pressure valves. In this picture you can clearly see that only means of safety available is the open vent which deals with any expansion (sometimes caused by over heating). There is no tempering valve, no expansion valve and no drip try. Its amazing that these copper cylinders can last up to 35 years without bursting. Usually the only reason they do end up bursting or rusting away is because the thermostat fails which results in the element overheating the water to 99 degrees and this puts more stress onto the tank resulting high level expansion and contraction cracking the weld. Quality of water is also a big contributor to rust and life expectancy of a copper hot water cylinder.
Has your cylinder burst before the recommended expectancy? Maybe its a good idea to investigate the cause before installing your new one to ensure your new hot water cylinder lasts much longer.