Kärcher HDS4.0/22 Dealer's Manual page 35

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
Karcher Liberty HDS Stationary Dealer's Manual 9.801-508.0 - AY
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 flame from
ignitor/sensor rod.
Faulty thermostat or water
temperature is too high
SOLUTION
Set test meter to 24 volt scale.
With pilot flame 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 flame 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 flame 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 flame impingement on the
ignitor/sensor.
If pilot flame is small and draft condition pulls
flame from ignitor sensor rod, the burner will turn
off and then on again. a. Adjust pilot flame higher
or clean pilot oriface. b. Bend ignitor/sensor rod
closer to pilot flame.
If flame 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 flame set too high will also cause burner to
short cycle. Pilot flame lifts over ignitor/sensor.
Maintenance
35