Justin, steel tanked Hot Water Systems (HWS) (like yours) have a plug in the top centre of the tank, there should be a removable plastic cover (plug) in the top outer casing. The plug in the tank has a sacrificial anode attached to it, it should be checked every 2 years (or more with a corrosive water supply) and replaced as necessary. The pressure valve should be flushed regularly to make sure it isn't blocked, I have seen half a house blown away by exploding HWS. It has been known for Wasps to build their mud nests in the drain pipe, blocking them, as I live in the country (plenty of Wasps) I don't have a drain pipe that can get blocked, I test my pressure relief valve every time I walk past the HWS, better safe than sorry, whenever you are doing any work on the HWS always have the relief valve in the open position, Regards Frank.

