Williams 2903511 Installation Instructions And Owner's Manual page 21

Troubleshooting Step 3
Point 5 (Z1)
Z1 is open and no ignition.
Check wiring and connections. If
everything is okay, replace the switch.
Point 7 (M2)
M2 is closed and fan thermostat
temperature lower than 104 °F.
Check wiring and connections. If they
are okay, replace the thermostat.
Step 4
8. Check Z9 (Room
Close the thermostat
clockwise rotation.
9. Check M1 (Overheat thermostat,
automatic reset). The thermostat is
closed at a temperture lower than
140 °F.
10. Check S (Combustion
motor).
Troubleshooting Step 4
Point 8 (Z9)
After a clockwise rotation, the contact is still
open. Check wiring and connections. If they are
okay, and the room temperature is cold, replace
the switch.
Point 9 (M1)
M1 is open and fan thermostat temperature is
lower than 140 °F. Check wiring, connections,
gas pressure and fan motor. Clean fan blades
and air grids. If everything is okay, replace the
thermostat.
Point 10 (S)
S motor does not run. Check voltage, wiring and
connections.
If everything is okay, replace the motor.
Step 5
11. Check NP (Pressure switch).
12. Check electrical supply to flame control box
(120 V)
13. Check TR (electrical transformer)
(120V/24V)
14. Check EV1 (Min gas valve, 24V)
15. Check RP7 (ignition electrode)
16. Check RP8 (flame sensor)
17. Check EV2 (Max gas valve, 24 V)
Troubleshooting Step 5
Point 11 (NP)
NP contact is open and air blower ON.
Check wiring and connections. Check and clean
blower pipes.
Check and clean burner and flue gas pipe.
Clean blower.
If everything is okay, replace the switch.
thermostat).
with a
blower
24 V
20
120 V