- 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.