Recently, we have noticed that when we're using a faucet or the shower, the water will run normally at the set temperature for a 30-45 seconds. Suddenly, the water pressure increases slightly, the water gets cool (1 sec), then goes quite hot (1 sec) then back to normal for another minute or so. This cycle goes on for as long as we're running the water. We have a standard, electric hot water heater. It happens when there are no other demands on water (dishwasher, another faucet, etc.). Thanks for your response.