pasadena_commut
Well-Known Member
Does anybody know of a way to test that a water heater anode is working while it is installed? That is, that the galvanic protection is actually active and working at an acceptable capacity.
The usual advice is to pull the rod and inspect it. But pulling an anode rod is enough of a PITA that I think most people would just replace it at that point.
Because the anode is bolted right to the metal of the WH body it isn't possible to access the current generated by that galvanic circuit. It is possible to test that there is a low resistance connection between the rod and the WH body, but that would still be present even if the rod itself had completely disintegrated and only the nut remained.
I tried to think of a way to do this sort of test and came up with two possibilities. They both require that the WH have a brass drain valve which is not electrically insulated from the WH body and that has a straight tube on the drain end into which a piece of test metal would fit.
1. Electrical method:
Take a brass garden hose cap. Remove the ring washer, replace with a disk washer of the same size. Drill a 3/8" hole through the center of both. Obtain a 1/2" diameter piece of clean iron rod. Drill and tap a 7/32" hole in this rod to hold a 1/4" screw. Drill a 1/4" hole through another rubber disk washer. Fasten the rod into the cap with a 1/4" screw in the order: rod, flat washer with 3/8" hole, cap, flat washer with 1/4" hole, nickel washer, screw. Test that there is no electrical connection between the screw and the cap, and that there is a very low resistance connection between the screw and the iron rod. Turn off the inlet and open a hot water valve to drop the pressure in the tank. Screw this contraption into the drain valve and then open that valve. Hope it doesn't leak. Open the T&P valve and tap the drain several times to release any trapped air. Measure the voltage difference between the screw head and the cap. It should be on the order of several tenths of a volt. Measure the current. (Note, all sizes are just examples and would have to be adjusted to fit the drain valve.)
2. Corrosion method:
Like above, but omit the outer rubber washer so that the screw is electrically connected to the cap. Leave it installed with the drain valve open for a week (?) and then pull it and check for corrosion, there shouldn't be any. The control is to install the cap from (1), which will not be protected, and its iron rod should corrode.
The 2nd method is a direct measurement of corrosion protection. However, I wouldn't be thrilled about leaving a fully pressurized water heater with its drain valve open for an extended period and only a modified garden hose cap in place to contain the water.
The first method is safer, flood wise, and faster, but how to interpret the results? I suspect that if any part of the rod is functioning the same voltage would be seen. The voltage comes from the chemistry of the metals in the two rods and the water in between, but says nothing about how well that system is working. The current observed should decrease as the rod is used up, or obstructed by a layer of calcium carbonate. If this measurement was made when a new rod was first installed then subsequent measurements would indicate how well the rod was working. But that current could be tiny, I suspect in the microAmpere range, possibly even lower. Typical multimeters have a lower range of 200 mA, and couldn't resolve it.
The usual advice is to pull the rod and inspect it. But pulling an anode rod is enough of a PITA that I think most people would just replace it at that point.
Because the anode is bolted right to the metal of the WH body it isn't possible to access the current generated by that galvanic circuit. It is possible to test that there is a low resistance connection between the rod and the WH body, but that would still be present even if the rod itself had completely disintegrated and only the nut remained.
I tried to think of a way to do this sort of test and came up with two possibilities. They both require that the WH have a brass drain valve which is not electrically insulated from the WH body and that has a straight tube on the drain end into which a piece of test metal would fit.
1. Electrical method:
Take a brass garden hose cap. Remove the ring washer, replace with a disk washer of the same size. Drill a 3/8" hole through the center of both. Obtain a 1/2" diameter piece of clean iron rod. Drill and tap a 7/32" hole in this rod to hold a 1/4" screw. Drill a 1/4" hole through another rubber disk washer. Fasten the rod into the cap with a 1/4" screw in the order: rod, flat washer with 3/8" hole, cap, flat washer with 1/4" hole, nickel washer, screw. Test that there is no electrical connection between the screw and the cap, and that there is a very low resistance connection between the screw and the iron rod. Turn off the inlet and open a hot water valve to drop the pressure in the tank. Screw this contraption into the drain valve and then open that valve. Hope it doesn't leak. Open the T&P valve and tap the drain several times to release any trapped air. Measure the voltage difference between the screw head and the cap. It should be on the order of several tenths of a volt. Measure the current. (Note, all sizes are just examples and would have to be adjusted to fit the drain valve.)
2. Corrosion method:
Like above, but omit the outer rubber washer so that the screw is electrically connected to the cap. Leave it installed with the drain valve open for a week (?) and then pull it and check for corrosion, there shouldn't be any. The control is to install the cap from (1), which will not be protected, and its iron rod should corrode.
The 2nd method is a direct measurement of corrosion protection. However, I wouldn't be thrilled about leaving a fully pressurized water heater with its drain valve open for an extended period and only a modified garden hose cap in place to contain the water.
The first method is safer, flood wise, and faster, but how to interpret the results? I suspect that if any part of the rod is functioning the same voltage would be seen. The voltage comes from the chemistry of the metals in the two rods and the water in between, but says nothing about how well that system is working. The current observed should decrease as the rod is used up, or obstructed by a layer of calcium carbonate. If this measurement was made when a new rod was first installed then subsequent measurements would indicate how well the rod was working. But that current could be tiny, I suspect in the microAmpere range, possibly even lower. Typical multimeters have a lower range of 200 mA, and couldn't resolve it.
