On our last road trip to the Oregon Dunes, we discovered water dripping down from behind the access panel on our water heater. Upon inspection, we discovered that the temperature and pressure (T&P) relief valve was leaking. I was fortunate that one of our group, John Duncan, is a plumber by trade and was more than willing to help me with the repair.
First, John asked me if the hot water temperature had seemed hotter than normal on prior trips before assuming that the relief valve itself has malfunctioned. If the water is hotter than normal, it can be an indicator of a problem in the thermostat or control system. In that case, the relief valve is doing exactly what it is designed to do--and that is why it is there. Since my answer was no, the temperature had not been abnormally hot in the past, we proceeded to the nearest hardware store for a new T&P valve.
On the way, John explained that a T&P valve monitors the temperature and pressure inside the water heater tank. When either exceeds the rating on the relief valve, the valve will open and relieve the excess pressure or temperature. Most T&P valves are designed for a temp of 210° and/or 150 lbs. pressure. John recommends removing the old valve and taking it with you to match the length of the temperature probe as well as the length of the valve neck to be certain you can close the access panel once it has been replaced.
After finding and purchasing the $12 valve, we followed these instructions:
1. Turn off the water heater.
2. Open a hot water faucet until the water runs cool. This will give you a cooler and safer water heater to work with.
3. Shut off the water pump.
4. Cover the electronics behind the access panel to prevent water damage.
5. Release the pressure on the water valve by lifting the silver lever on the front of the valve and drain until the water flow stops.
6. Remove the old valve with a pipe wrench.
7. Wrap the new valve threads with Teflon tape (or you could coat with TFE paste--John prefers to use both) or any pipe thread lubricant that is approved for potable water
8. Make certain the T&P valve fitting on the tank is clean and free of residue from the old valve.
9. Screw new valve in until tight.
10. Turn on the water pump to refill the water heater tank and check for leaks.
11. Turn on the water heater and, once the heating cycle is complete, check for leaks again.
John made it a point to stress that UNDER NO CIRCUMSTANCES should a relief valve ever be plugged or capped so that it cannot relieve excessive pressure or temperature, even as a temporary solution. It is better to have a leak rather than an explosion.
In the end, the problem with my T&P valve turned out to be calcification, a common problem but not particularly harmful to the water heater. Since the repair, I have not noticed the water pump turning on sporadically to maintain pressure in the pipes. An annoying occurrence that I had not been able to diagnose for months has been remedied by eliminating this leak.