What in the world is a TPR valve?


For many of us, water heaters are one of the unsung heroes of day-to-day living.  Quietly, tucked away out of sight, water heaters help us bathe and wash whatever needs bathing and washing.  These appliances do two simple things really well.  First, water heaters heat up water.  Second, water heaters hold the heated water in an insulated tank until it is needed.  When water inside the tank is heated, the pressure increases. As warm water is used from the tank, cool water enters the tank and is heated.  This repeating cycle includes dynamic pressure variations.  This is where the Temperature/Pressure Relief (TPR) Valve comes in.  The TPR valve has an important role in the safety of your home.  

Remember I mentioned rising and falling pressures?  There is a possibility the heating element logic could malfunction, which in turn would heat the water to boiling temperatures.  Without the TPR valve, pressures would build enough to cause a powerful explosion.  The TPR valve is pre-set from the manufacture to protect against dangerous temperatures and pressures.  If the pre-set condition is met, the TPR valve opens to let out the hot water/steam and relieve the pressure inside the tank.  Understand that water expands approximately 1,600 times its original volume when turned into steam. 

The above photo is a recommended installation displayed by AO Smith.  Some generic instructions for the TPR valve is to have the probe in the top 6 inches of water.  The valve needs a discharge tube attached to it.  The tube should be a material that can handle temps up to 250 Degrees Fahrenheit. The tube should terminate a maximum of 6 inches above the ground or outside the building.  If in cold climates, terminate indoors to keep the tube from freezing up and becoming clogged.  Never cap the discharge tube or reduce the diameter of it.  

There are different recommendations for the inspection of the TPR valve, so I will insist on you reading the owners/installation manual to get the particulars for your unit.  Please check the credibility of the person installing your water heater.  Below is an example of an average install by a "licensed" plumber I've seen during an inspection.  I guarantee you will quickly find some things wrong with this TRP discharge tube!  Remember to always read the manufactures manual for the unit you have in your home.  The manual has the specific inspection and installation requirements for your water heater. If you are in doubt or need any assistance give Ellis Home Inspections LLC a call.              

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