Re: High Pressure/releif valves - again?
Posted by Jim Riehl on September 04, 2002 at 01:24:15:
In response to Re: High Pressure/releif valves - again?
: We replaced a 15 year old water heater 6 months ago. Things were fine until two weeks ago when the pressure relief valve released. I've checked the thermostat - turned the temps down and up etc. that is working just fine. The city did some hydrant/water repair in our street about the time this happened. The relief valve continued to release every few days so I replaced the pressure relief valve thinking a one time surge damaged it but then it happened again. The city denies having changed the pressure - but they are telling me my new pressure relief valve is faulty and at the same time telling me to install a pressure reducer. Seems to me that if my valve is faulty the reducer won't help and if my valve is ok - the pressure has changed and they are lying. My question is if my house pressure is at 80 psi - how would that trip a relief valve calibrated to 150 psi? How accurate are those valves? Are they "junk" as the city so eloquently told me? Is there a brand or type that is the best? I don't want to spend $200 + on a reducer if a $6 valve is my real problem.

the thing you have to understand here is that the valve you are referring to is actually a "temperature AND pressure relief" valve (or T&P valve). the valve is designed to open to the atmosphere when the temperature is too high, or the pressure inside the water heater exceeds a set limit. the reason for this design is that the boiling point of the water is decreased when the pressure on it increases. the higher the pressure in the tank the lower the boiling point of the water. i've seen water boil at room temperature in a near vacumn in a bell jar in a lab. that's a very dangerous situation, since if you allow the pressure to increase beyond a certain point you could have a "runaway" water heater that can actually explode in your house (the entire contents of the water heater "flashes" to steam in less than a second). the water heater temperature setting you are using is probably much too high (water over 120 degrees is a scald hazard) so you need to set the temperature somewhere around the mid-way mark on the thermostat and gradually increase it from there. when the temperature at a water outlet near the tank reaches 120 degrees (measured by a thermometer) you should leave it there and see if the the valve continues to "blow off". if it won't hold, call the manufacturer and ask for help. the fact that the city did any work near your house doesn't have anything to do with your problem and the water pressure in your house would have to exceed 190 psi static pressure to trip the T&P valve by itself.

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