Thanks for the reply Randy,
1. pressure 35 to 50 psi, depending on the time of day.
2. Thermal expansion doesn’t seem to be an issue: no dribbling or signs the T & P valve is leaking or subject to high pressure.
3. Haven’t checked an anode but when the elements on the last heater failed and I had to replace them there wasn’t much left to them. There was two stubs about three inches long on the lower element and a heavily corroded open loop in the top element. This was after about 16 month in service.
Some kind of corrosion is taking place, but why?