Hot Water Temperature Varies

Depends on what was done before you had your shower.
If you did a couple of loads of wash or followed someone else who showered, your water heater is just not keeping up with the demand.
How old is it?

Outside water temperature. The shower mixes "cold" water from outside the house with hot water from your water heater. The hot water is around 120 deg F and is controlled by a thermostat. The outside water is whatever it is. When I was growing up in the deep South, the outside water temperature in the summer was 80+ degrees. I just needed to crack open the hot water to get good bath temperature. In the winter, outside water temperature would drop to the 50's so much more hot water was needed.

As noted in the previous post, if your hot water heater is cold because you've used up all the hot water or because the thermostat is off, that is another issue.

I don't think seasonal changes can account for daily differences like these, Engineer. My first guess is a faulty thermostat but I've never seen a thermostat do this. My next guess, poltergeists.

That's just the way they work, msmarg. Maintaining a constant temperature would be more complex and more expensive. Rather than heating the water continuously, the gas or electric comes on a a preset point, and continues to heat it till the high temperature limit is reached.

If you run a bit of hot water before showering, it should kick in, and give you a nice hot shower.

I don't think that's quite right, Roger. Water is heated to the temperature that the thermostat is set at, I believe the factory setting is around 140 degrees F. If there has been no pull on the hot side for a period of time, the entire tank volume will be heated pretty close to the set thermostat temperature.

A water heater never heats to the hi-limit point unless there's a malfunction at the junction. Then the pressure-temperature relief valve opens and some pretty scary stuff blasts out.

I'm having the same problem with my gas tank. First thing in the morning it can be scalding hot or merely lukewarm. My tank is fairly new so surely there is not a temperature gauge problem?

This sounds like a normal operating condition.

If you don't want scalding hot water, dial down the thermostat on the side of the tank. If the water is lukewarm at a faucet, let it run briefly till the water temp drops to the low limit, at which point the gas or electric element cycles on. It will then heat the water to the high temp setting.

That happens to me everyday but that’s because I have one of those tankless water heaters, boy I’ll never have one of those again!

I didn't realize this thread started in 2009, she probably has a new water heater by now

What mixing valve are you referring to, and why does a bad mixing valve call for an element replacement. I would be extremely displeased if any part of a hot water system required replacement after only two years.