Just a heads up for anyone in Auckland who's had to deal with their hot water cylinder acting up - check the pressure relief valve first. Mine was constantly dripping and the plumber wanted $200 just to look at it. Turns out a bit of grit had it stuck open. Gave it a gentle wiggle with a pair of pliers, let a bit of water out to flush it, and it's been good as gold for six months. Saved a packet and it took five minutes.