Endurance
Page 37
Failure of the water flow switch to operate
during a hot water draw prevents boiler water from
flowing through the DHW heat exchanger and therefor
the DHW will not be heated.
To test the switch, place a
temporary
jumper
across the flow switch terminals. If the internal pump
operates and there is DHW generated then the water
flow switch is faulty and must be replaced. Note:
Switch orientation is critical for proper switch
operation, The identification plate on the switch must
face up and the arrow on the plate must point in the
direction of flow.
Failure of the mixing valve will allow cold water
to be mixed with the hot water from the DHW heat
exchanger during a DHW draw regardless of the
setting of the mixing valve or the temperature of the
water leaving the DHW heat exchanger. The failure
can be detected by observing the temperature of the
three pipes connected to the mixing valve. If the “mix”
temperature is luke warm or cool and the “hot”
temperature is hot and the “cold” temperature is cold
then the mixing valve is either faulty or incorrectly
adjusted and must be replaced or adjusted.
DHW heat exchanger scaling may occur in some
areas of the country where there are high
concentrations of minerals in the water. These
minerals may cause fouling of the DHW heat
exchanger over an extended period of time (lime build
up). Other minerals, which react more quickly in well
systems (mostly magnesium), cause slime on the
inside of the heat exchanger and prevent adequate heat
transfer. These minerals must be filtered out by a
special incoming water filter or by the addition of an
inhibitor to protect the coil and provide acceptable
water quality. Minerals may be removed when
necessary by flushing the coil with a cleaner such as
“Unlime®” or “Sizzle®”.
11.5 High Gas Consumption
Boilers operating with an improper air/fuel ratio
are very inefficient and consequently, have very high
gas consumption. Because efficiency is high when the
CO
2
is high, boilers operating with low CO
2
(especially LP boilers) consume more gas. Adjust the
CO
2
or O
2
for optimum efficiency. If no combustion
analyzing equipment (CO
2
or O
2
) is available then a
proper adjustment of the air/fuel ratio (CO
2
) can not
be accomplished. However, by briefly sniffing the flue
gases it is possible to determine if the CO
2
or O
2
is
within the proper range. There is no significant flue
gas odor when combustion is proper. A strong
piercing smell indicates poor combustion and
generally a lean mixture (low CO
2
). Check gas valve
calibration (offset adjustment) and adjust if indicated.
Do not attempt to correct combustion by reorificing
without an O
2
or CO
2
kit.
