I am having issues with my Water Heater. It's a slantfin tankless boiler (TR-30 PT). It's running on a 4 zone setup. I typically only use one of the zones though. We've been in the home for a year and a half. Towards the end of this winter I started finding a few gallons of water draining from the T&P valve every few days.
I tested the expansion tank and found it to be leaking water from gauge, leading me to believe the diaphram has ruptured and we needed a new one. I bought the same model replacement. An Amtrol #60 and gauges to test our home water pressure and PSI on tank. I attached the water meter to our outside hose line and read about 56 PSI. I then took the precharged (to 12 PSI) new tank and charged it further up to about 55 PSI before installing it. I then removed the old expansion tank to find it almost completely filled with water. Replaced it with the new tank. Turned water line back on and power to water heater. Gave it a day or so.
Now I'm still seeing water, perhaps more. So, even though the exp tank was shot, what else could be causing this? Autofill valve? I don't think the T&P valve is bad as it is draining water once the meter reaches the max level on the valve which is 30 PSI. The slantfin temp range was set at 160 – 180. I lowered this to 140-160 and still same issue.
I then turned on the water from my faucet for a while, and the pressure on slantfin was hovering between 2 and 10. Got the temp on slantfin below 140, down to 120ish. It didn't seem to instantly turn back on, but then turned on the first floor of our home (ZONE 1 of 4), slantfin initiated and watched the gauge on the unit. As it heated the water from 120 to 140 (where min is set) it gradually increased pressure until right about hitting 140 the pressure then hit 30 PSI and T&P valve started draining.
Should I not have charged the new tank? I was under the understanding this needed to be same if not a few PSI below water pressure. Does this change if on a multi-zone house. If using a tankless system?
Should my T&P valve be rated to take on more pressure than 30 PSI?
Should the precharge be the same as the water supply line even if the tank will be placed after a "water pressure regulator valve" set between 12-25 PSI?
Any information would be greatly appreciated. I'm stumped…
Best Answer
The tank should be charged to the pressure at the attachment point. If the tank is attached to a point in the system where the pressure is supposed to be 25 psi, the tank should be pre-charged to 25 psi. If the tank is attached to a point in the system where the pressure is supposed to be 55 psi, the tank should be charged to 55 psi.
When the water pressure raises above the air pressure in the expansion tank, the water will begin to fill the tank and compress the air further. As the water pressure decreases, the air pressure in the tank forces the water out of the tank. If the tank is charged too high, water will not be able to compress the air and fill the tank.
Note: Measuring the pressure in the tank while it's connected to a pressurized water system, will show the pressure in the water system not the pre-charged air pressure of the tank. To measure the air pressure of the expansion tank, you must isolate it from the system.