LAARS EDN Series - Installation, Operation and Maintenance Instructions - Manual (Page 37)

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.