Water Heater Randomly heats water.

[Petey]

I was wondering if anyone knows what could be wrong. My water heater seems to heat water only after someone tries to use hot water. For example, the first person who takes a shower in the morning has luke warm water, but the people who take showers about an 1 hour after have really hot water. It seems like if someone does use the hot water for a while then it shuts down and then once someone requests hot water, it turns back on. I checked and it's not an energy saving technique. Does anyone know what could wrong? It's been doing this for as long as I've lived here (about a year).

[Doug]

It would help if you gave us more details like, is it a gas fired or electric water heater?

In any event, I've seen this in a vacant cottage that I have. The water remains lukewarm from this gas water heater. After there's been some draw down, the heater brings the water up to full temp.

What I think is happening in my case is that the main gas valve is sticking. This is the valve with the thermostatic temp control. I had the gas shut down to it over the summer and after being relit, the problem was even worse. I suspect that the valve gets gummy with age and or sediment buildup from sediment and moisture in the gas line.

The solution? Replace the gas valve. However since the price of just a new gas valve is about half the price of a new water heater, I suspect that the best bet is to replace the heater, especially if its got some age on it. In the meantime, try simply turning up the temp on the valve thermostat.

Doug

[Trajen]

I suspect your WH problem is caused by the hysteresis properties of the temperature switch. I found the following info at wikipedia...

Hysteresis can be used to filter a signal so that the output reacts slowly by taking recent history into account. For example, a thermostat controlling a heater may turn the heater on when the temperature drops below A degrees, but not turn it off until the temperature rises above B degrees. Thus the on/off output of the thermostat to the heater when the temperature is between A and B depends on the history of the temperature. This prevents rapid switching on and off as the temperature drifts around the set point.

[Petey]

Thanks guys, It's a gas water heater and the house and water heater are only 4 years old. I don't have the make and model of the water heater on me right now, but I can get it. I've already tried turning up the temp on the valve, but that doesn't seem to make any difference.

Is there a way to find out if my temperature switch has hysteresis properties? I looked at the water heater manual and I didn't notice anything about this.

[Speedy Jim]

The hysteresis is built into the gas control to avoid frequent cycling of the burner.

They are something less than a "precision" device though and c hanges like you are seeing do occur over time.

The control is not "repairable". You can, however, replace the gas control. Or, at least someone can. A heater which is 4 years old may be worth investing a new control in, considering what heaters cost today. You do the legwork to find out what it would cost for a new control where you live.

Jim

[George E. Cawthon]

I think you are just screwed. My gas water heater does the same thing, but it is due to the great difference between turn on and turn off temperatures. I don't know about the hysteresis stuff, but if you look at an attic thermostat you will find that it has a 10-15 degree differential between turn on and turn off. My gas WH has at least a 10 degree and maybe more differential. Previous info on this group indicated that it is quite common with gas heaters. My previous electric water heaters only had a 2-3 degree differential. I still have the thermostats out of an earlier one (finally eroded a hole an leaked) which I tested thoroughly in preparation for use in a different application. There is no guarantee that a new one won't have a large differential also.

[Don Young]

As other posters are mentioned, your situation is normal and intended. You just have to find a compromise setting where the water is a little too hot sometimes and not quite hot enough at others. This characteristic is intended to reduce cycling of the burner and thus conserve energy.

Don Young