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VZ-VZH-VZT-IOM (08-24) 1047121-A
Combination Gas Valve Maintenance
⚠ WARNING ⚠
The combination gas valve is the prime safety shutoff. All gas supply lines must be free of dirt or
scale before connecting them to the unit to ensure positive closure.
Inspect the combination gas valve, carefully remove any external dirt accumulation, and check wiring connections.
Check the valve annually to ensure that the valve is shutting off gas flow completely as follows:
1. Remove burner cabinet panel(s) for access:
a. For models VZ and VZT, disconnect combustion air piping from blower if unit is connected to outside combustion
air, unplug blower motor power cable, and remove top blower panel with blower and motor assembly attached.
b. For model VZH, remove side panel.
2. Close manual shutoff valve to prevent flow to combination gas valve.
NOTE: Use a water column manometer that is readable to the nearest tenth of an inch.
3. Connect manometer to 1/8-inch outlet pressure tap on combination gas valve.
4. Open manual shutoff and combination gas valves.
5. Use finger to fully block main burner orifice for several seconds.
6. Observe manometer with orifice blocked. If any pressure is indicated, combination gas valve is leaking and must
be replaced before heater is restored to operation.
7. Re-install panel(s) removed in step 1. models VZ and VZT, reconnect combustion air piping to blower if unit is
connected to outside combustion air and plug in blower motor power cable.
Ignition Control Module Replacement
1. Turn OFF electric and gas.
2. For models VZ and VZT, open hinged access door. For model VZH, remove side panel.
3. Unplug ignition control module wiring harness.
4. Remove and save screws that secure ignition control module and remove control module.
5. Install replacement ignition control module and secure using existing screws.
6. Plug in ignition control module wiring harness.
7. For models VZ and VZT, close hinged access door. For model VZH, re-install side panel.
8. Turn ON electric and gas and check for proper operation.
Pressure Switch Replacement
1. Turn OFF electric and gas.
2. For models VZ and VZT, open hinged access door. For model VZH, remove side panel.
3. Unplug pressure switch wiring harness.
4. Disconnect pressure switch tubing.
5. Remove and save screws that secure existing pressure switch and remove switch.
6. Install replacement pressure switch and secure using existing screws.
7. Reconnect pressure switch tubing and wiring harness.
8. For models VZ and VZT, close hinged access door. For model VZH, re-install side panel.
9. Turn ON electric and gas check for proper operation.
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