Gas Hot Water Heater T-P valve problems
I need some help with a plumbing problem. My company has a 138 unit complex of rentals only 6 years old consisting of 3 story high modules equipped with gas fired hot water heaters for each unit. In the last 3 weeks, they have experienced 3 different apartments with the T-P valves blowing off slightly to a whole lot of flow out the overflow tubes. The system pressure I measured today was 70 psi and a water temp. in the kitchen of 130 F. This safety valve was losing lots of water over the weekend which drained out on the ladies deck and ran down into the basement garage under the unit. The incoming supply line from the city water supply has a surge tank with some compressed air still in it that is tapped into the cold water feed line serving the heater. Why, all of a sudden are these T-P safety valves letting loose? After blowing out the valve and reducing the pressure, the valve did reseat O.K. and the tank re-heated and shut down as designed. The pressure measured at the drain down valve never exceeded 70 psi. Anyone run into this situation or am I just the lucky one?????
Replies
A 2% failure of T&P valves, if the failed, after 6 years, is not a problem, just the reality of maintenance in a 100 plus unit facility. T&P valves are relatively inexpensive, buy a few and the next one that lets go, replace it. You may want to consider routing the discharge piping in a more suitable manner, like to a drain, not a deck.
Is there a pressure regulator on the system? Is there a pressure booster in the system? Was there any pattern to the locations of the valves that let go? Are the valves that let go rated the same as the other 135? What is the T&P rating(s)?
Check the surge tank and make sure it's not waterlogged. It needs more than just a little air in it to do its job.
Also, you might want to consider installing a pressure reducer (or adjusting the one you have). 70 PSI is a mite on the high side.
70 PSI is a little high but what happens here if you have a pressure reducer or a backflow check valve in the line, as the water heater heats the water, if no water is being used at the time, the heated water will expand as it heats up and the pressure can increase quite a lot and cause T&P valve to vent off. This usually just causes small flow dripping of the T&P valve but you might have the kind that opens fully and won't shut off until reset.