Water heater/bomb!

Many of the conveniences of modern living come at a price.  Sometimes the price has been paid by those who preceded us.  I am talking about risks and dangers that were discovered by accident (pun intended.) People have been hurt or killed before the dangers were realized. 
After accidents happen, we think of ways to prevent these accidents form happening again so others won't have to pay the price again. 
One of the conveniences we take for granted is running water; running hot water.  In order to have running hot water, the water has to be heated and pressurized. 
It is physically possible to heat pressurized water to a temperature higher than its normal boiling point.  If that is done, the water would instantly turn to steam as soon as the pressure is lost.  Steam takes up about 1600 times more volume than liquid water so water suddenly turning to steam in effect is an explosion.
The temperature to which the waterheater heats water isn't anywhere close to the boiling temperature, however, sometimes mechanical devices fail and the water gets super heated; heated above its normal boiling point.  If the water heater tank breaks because it can no longer endure the increased temperature and pressure,  an explosion happens.  Calling it an explosion is not an exageration.  Just do a Google search on water heater explosion.  Here is a picture of the damage done by an exploding heater in a school building.  (You can read about it here.)

To prevent this from happening, a valve is installed that releases water from the tank when the temperature gets too high and also if the pressure gets too high.  Two safety measures in one devise.  This devise is called a Temperature Pressure Relief Valve (TPR Valve.)  Water heaters have a fitting somewhere near the top and upon shipping usually the TPR valve is installed already so forgetting to install it is ruled out. 
This is what a TPR looks like. 

On the right you see a diagram showing a typical location of the TPR valve.  Another common location is through the top of the tank.  They are always somewhere near the top.

At a recent inspection near Kitchener, I saw a water heater that didn't have a TPR valve. The strange thing was that it didn't even have place to install one.  A manufacturer's oversight?  No.  On the data plate from the manufacturer it was noted that this tank had a temperature limiting device behing the upper access panel. (On the diagram you can see this panel right below the Electrical supply.)  So one of the safety features has been looked after by the manufacturer. 
What about the pressure relief part of a TPR Valve?  Well...it was overlooked by the installer.  (I hope the installer wasn't a licenced plumber.)  A pressure relief valve has to be installed somewhere in the water line near the tank. It doesn't have to be in the top; that is only for the temperature aspect of a TPR, but it HAS to have one.  I recommended to my client to have a licenced plumber rectify this safety issue.  Doing this would turn a waterheater/bomb into a waterheater.

Submitted by Bert, for Benchmark Home Inspection Services.  Your Kitchener, Waterloo, Guelph and Orangeville area home inspector.