I forgot to mention the HWH electric motor is grounded by the 2 mounting screws. And over time these screws get grimy and no longer make a good ground. So if you are pushing buttons and nothing happens, maybe you should take out those two 5" long screws and add a ground wire. (Be sure you find a good ground using the continuity option on your voltmeter.) See pictures below.
This summer I added an extra ground wire to avoid getting stuck somewhere, someday. Call it good Preventative Maintenance (PM) everyone should consider doing someday soon.
Also, if your HWH fluid is 8+ years old you probably should replace it with straight Dexron III, I.e., get the basic stuff with no "High Mileage" additive in it. It only takes 7 quarts and if you use a 12V Scavenge Pump ($18) you will find this to be an easy service.
If this does not work,
and if you check your fuses and they are okay, then maybe you need to remove your HWH control board and send it to HWH for service? First I would check to see if your HWH button is not making a good ground. To test for this you just need a Circuit Test Prob and...
1) Attach the test probe to ground and
2) Touch the probe tip to the back side of the HWH switch you think maybe bad. This will complete the circuit to ground and if your HWH system starts to work, then you know you need a new HWH face board.
Please let us know what you find?