Page 54
VI − TROUBLESHOOTING
IMPORTANT
Normal setup conditions of a new unit installation re
quire running the unit through several tries for igni
tion before the unit will run continuously. Initially the
unit may start and die several times until air bleeds
from gas piping. Break and remake thermostat de
mand to restart ignition sequence at 2 to 3 minute in
tervals until continuous operation is obtained.
Effective troubleshooting of the G21/GSR21 depends on a
thorough understanding of all unit components and their
function as described in this manual. The main trouble
shooting categories are:
Unit Will Not Run Electrical Checks
Unit Will Not Run Ignition Control Checkout
Unit Will Not Run Gas, Spark and Air Checks
V" Blower and VSP1/2 Troubleshooting
Unit Sputter Starts And Dies.
Unit Starts Clean But Runs Less Than 10 Seconds.
EACH OF THE PROBLEM CATEGORIES ARE BROKEN
DOWN INTO TROUBLESHOOTING FLOWCHARTS LO
CATED IN section VII TROUBLESHOOTING FLOW
CHARTS in the back of this manual, with additional infor
mation provided to explain certain checks. Steps in the flow
charts for measuring manifold pressure, flame signal, ex
haust CO
2
content and exhaust CO content and operating
input are explained in previous sections.
CHOOSE THE FLOW CHART THAT BEST DESCRIBES
THE UNIT’S PROBLEM. FOLLOW THE FLOW CHART
STEP BY STEP. At any point a NO" answer is reached and
a repair is made, reassemble the unit and retest for opera
tion. If unit does not operate, recheck that point and then
continue through the chart. Occasionally more than one
specific problem may exist.
When troubleshooting a unit, be sure that all basic checks
are covered carefully. Double check your diagnosis before
replacing components. DO AS LITTLE DISASSEMBLY AS
POSSIBLE during troubleshooting to prevent introducing
additional problems such as gas or air leaks or damage to
components.
WARNING
If unit has been operating, internal components will
be HOT. Allow unit to cool for at least 15 minutes be
fore placing hands into the heat section opening. To
completely cool to room temperature, the blower
should run continuously for about 40 minutes.
A − Safety Shutdown
Safety shutdown occurs when any of the problems are en
countered.
1 − Loss of combustion during a heating cycle caused by:
a − Obstruction to air intake piping;
b − Obstruction to exhaust outlet piping;
c − Low gas pressure;
d − Failure of gas flapper valve;
e − Failure of air flapper valve;
f − Failure of main gas valve;
g − Loose spark plug or sensor creating pressure loss;
h − Loose sensor wire;
i − Watchguard normal operation;
j − Modulation control normal operation V" only
singlestage heat.
2 − High limit cutout:
a − Blower failure;
b − Temperature rise too high;
c − Restricted filter or return air;
d − Restricted supply air plenum.
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