Bellingham Home Inspections (King of the House): Temperature Pressure Relief Valves

The Temperature pressure relief (TPR)  valve, and the drain line, are among the most misunderstood safety devices in all of plumbing. Why is a missing or incorrectly plumbed TPR a critical safety issue?  The simple answer is that it is the primary defense between residents of the home and an exploding tank. As a Bellingham home inspector, in my area at least, I would say that about 30 percent of the time, the drain line is defective -- installed wrong. Usually it is routed up. But sometimes it is the wrong material, like PVC (only acceptable for cold water) or a coiled up garden hose serving the hot water. Other times there is no drain line at all so a discharge of hot water would be directed into a room or straight out. People, who know no better, will argue that it does not matter if it goes up -- steam will be discharged in an emergency. The problem there is that, periodically, these devices might operate to relieve instances of high water pressure. If the system is correctly plumbed that is a very rare occurrence, but if it is a closed system with no expansion tank and a pressure reducer, the TPR might drain some when lots of hot water is being produced. If that happens, we are not talking about big bursts of steam, just a half a cup or so of water running out. But, if the drain runs up, this quantity of water, that is routed by gravity, stays in the pipe down by the TPR valve. Over time, that can clog the valve mechanism so, when the big one comes -- it is locked shut. If that happens then you are in trouble. The tank below is unsafe!

• King of the House
• Bellingham MLS

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