Water Heater Safety

Many consider the water heater to be the most dangerous device in your house. Water heaters are equipped with a temperature- and pressure-relief valve (usually abbreviated TPV or TPR) that releases both hot water and built-up pressure if either gets too high (usually 150° F, or 300 pounds per square inch/psi). If the valve malfunctions, the heater can explode. Carefully test your valve periodically by quickly tripping its test lever. If water pours out of the discharge tube, the valve is clear of deposits and capable of performing its job. If it has been a while since you've performed this test, or if the valve is old, be aware that it might become stuck in the open position during testing. Before you begin, know the location of your main water shutoff, in case this happens.

It would be wise to have someone on standby at the main shutoff. You should also have a shutoff at the water heater.

Do not try this if your TPR valve is not plumbed properly.

The discharge piping serving a TPR valve should:

1. Be constructed of an approved material such as CPVC, copper, polyethylene, galvanized steel, polybutylene, polypropylene, or stainless steel.
2. Not be smaller than the diameter of the outlet of the valve it serves (usually no smaller than 3/4").
3. Shall not reduce in size from the valve to the air gap (point of discharge).
4. Be as short and as straight as possible so as to avoid undue stress on the valve.
5. Be installed so as to drain by flow of gravity.
6. Not be trapped since standing water may become contaminated and backflow into the potable water.
7. Discharge to the floor, to an indirect waste receptor, or to the outdoors. 
8. Not be directly connected to the drainage system to prevent backflow of potentially contaminating the potable water.
9. Discharge through a visible air gap (atmosphere) in the same room as the water heater.
10. Be first piped to an indirect waste receptor through an air gap located in a heated area when discharging to the outdoors in areas subject to freezing, since freezing water could block the pipe.
11. Not terminate more than 6 inches (152 mm) above the floor or waste receptor.
12. Discharge in a manner that could not cause scalding.
13. Discharge in a manner that could not cause structural or property damage.
14. Discharge to a termination point that is readily observable by occupants because discharge indicates that something is wrong.
15. Be piped independent of other equipment drains, water heater pans, or relief valve discharge piping to the point of discharge.
16. Not have valves anywhere.
17. Not have tee fittings.
18. Not have a threaded connection at the end of the pipe so as to avoid capping. 
    

If you don't think your up to this type of testing call a trusted plumber. If the water heater is old you may want to have the TPR valve replace while you have the plumber on-site.