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Q.After reading the article "Using Water Heaters for Radiant Heat" (11/98), I decided to replace my boiler with a 75-gallon propane water heater. In general, this is working great, except that about every three weeks the pressure-temperature relief valve, which is rated at 210°F, keeps tripping. I live in the cold climate of Michigan, and I need to keep the water heater temperature set on "High," which is about 180-190°F. When the relief valve trips, I notice that the water temperature is about 195°F. What’s going on?

A.Heating contractor and JLC author Bill Clinton responds: Although most residential water heaters have a maximum setting of 160°F, there are some heaters that are factory-equipped with 180°F thermostats. I have used a number of these, without having the problem you describe.

When the burner on a water heater turns off and there is no circulation happening, hotter water can stratify at the top of the tank, resulting in higher temperatures than the thermostat setting. Perhaps this is the cause of your readings. If you are sure that your temperature reading is accurate, I would turn down the setting a bit and try installing a new relief valve. Under no circumstances attempt to operate a water heater without a proper relief valve.

What is likely is that you have a pressure problem and not a temperature problem. Thermal expansion may be forcing the relief valve open. Do you have an expansion tank installed? If so, is it big enough? Was its air charge adjusted to equal the household pressure before installing it? A pressure gauge attached to the drain of the water heater will help you determine if your problem is really excess pressure.

Finally, remember that temperatures this high can be dangerous. Unless you are well-trained and quite competent, don’t risk working with that water heater when it’s hot.