TPR Valves; A Ticking Time Bomb?
The temperature pressure relief valve or commonly referred to as "TPR valve" is a safety feature that is installed on water heating equipment. It is especially integral to the safe operation of tank water heaters. Typically the thermostat controls regulate the temperatures inside the heating tank and if the water temperature becomes too hot, the system will shut down. My water heater heater controls are designed to shut the heater down at 180 degrees F. But what happens if this system fails? That's where the TPR valve comes in. It's designed to release pressure/water in the event that temps and pressures within the tank exceed a certain limit. The industry standard is 210 degrees Fahrenheit and/or 150 psi.
But even these valves can fail possibly causing catastrophic damage if there is a deficiency in the tank. That's why it's important to test that valve a few times a year by simply pulling the toggle handle and making sure that water freely flows out of the drain pipe and then closes properly. Valves that are allowed to sit for years without movement of the parts will eventually seize up with sediment and mineral deposits especially if you live in an area with hard water like central Texas. Softened water helps, but that valve should always be tested regularly.
I used to be conscientious in testing these valves to the point that I was going to try and free the valve one way or another. The problem with this is that valves were not closing and sellers were not too happy having to do a repair they didn't expect to have to make. After explaining the importance of a properly functioning valve and the dangers, I was able to alleviate most annoyances. However, there was one seller in particular who wanted me to foot the bill for the repair claiming I broke the valve since it wasn't leaking before the inspection.
I still perform due diligence concerning the valve, but if I can't open it with a reasonable minimal amount of force, it gets flagged for further evaluation and repair by a qualified plumber. So make sure you test those valves regularly. It will help to keep you safe and make a home inspection go along more smoothly. Following are a couple of spectacular examples of what can happen if a water heater tank fails.
Real life event: