Kärcher HDS3.5/20 Operator's Manual page 24

PROBLEM
HAVE PILOT FLAME,
MAIN BURNER WILL
NOT TURN ON
SHORT-CYCLING
OF MAIN BURNER.
MAIN BURNER
TURNS OFF BEFORE
THE BURNER SWITCH
OR FLOW SWITCH
IS TURNED OFF
24
TROUBLESHOOTING
POSSIBLE CAUSE
Faulty main valve coil in the
gas valve
Faulty ignitor/sensor and/or its
wiring
Ground wire not attached to
machine chassis
Faulty ignition control unit
Draft condition pulls fl ame from
ignitor/sensor rod.
Faulty thermostat or water
temperature is too high
9.801-509.0 - C • Karcher Operator's Manual
SOLUTION
Set test meter to 24 volt scale.
With pilot fl ame on ignitor/sensor, probe terminals
MV and MV/PV on the ignition control unit. If you
read 24 volts here, but not at the gas valve,
there is a loose wiring connection. Repair or
replace as needed.
If you do read 24 volts at MV and MV/PV and
the pilot fl ame is impinging on the ignitor/sensor
rod, the problems may be:
a. Faulty ignitor/sensor and/or its wiring.
b. Faulty ignition control unit.
Set test meter to the ohm scale. Turn burner
switch off.
Check continuity through the green ground
wire and its connections.
Reconnect the ignitor/sensor wire and the
ground wire.
Turn burner switch on. With the pilot burning and
the fl ame on the ignitor/sensor rod, the main
burner should turn on. If it does not, replace the
ignition control unit.
Check the thermostat by bypassing at
terminals P1 & 1.
Set thermostat high. With main burner on,
observe the pilot fl ame impingement on the
ignitor/sensor.
If pilot fl ame is small and draft condition pulls
fl ame from ignitor sensor rod, the burner will turn
off and then on again. a. Adjust pilot fl ame higher
or clean pilot oriface. b. Bend ignitor/sensor rod
closer to pilot fl ame.
If fl ame impingement on the ignitor/sensor is
stable and the system short-cycles, check the
limit switch.
Set test meter to 110 volt scale;
a. When the system cycles off, probe
the switch terminals of the limit switch.
b. If you read 24V accross the switch
terminals the limit switch is open.
Replace the limit switch.
A pilot fl ame set too high will also cause burner
to short cycle. Pilot fl ame lifts over ignitor/sensor.