Unfortunately, as I have a 240A not the 240A2 I can’t dig through the data sent by the Navien to see what matches the values for the properties you mention.
So far, I have been able to determine that there are several counters - though I don’t know what they measure. I determined that they are counters as the low byte seems to increment over time, and when it ticks over 255 (0xFF) the high byte increments.
Water(28) + Water(29) is a counter
Water(30) + Water(31) is a counter
Gas(28) + Gas(29) is a counter - this one is tied to gas usage, as the more the gas is running the faster the increment.
Gas(30) + Gas(31) is a counter
Gas(33) + Gas(34) is a counter