LAARS Mighty Therm VW-PW (Sizes 175-400) - Installation, Operation and Maintenance Instructions - Manual (Page 25)

Mighty Therm Volume Water Heaters
Page 25
5. Attach one end of the manometer hose to the
fitting on the gas valve and the other end to the
manometer.
6. Open gas supply valve to the heater to test.
7. With the main burners firing, the manometer
reading should be between 6.5 and 9 inches W.C.
for natural gas, and between 11 and 14 inches
W.C. for propane units (see Table 6).
5.1.2 Checking the Manifold
Regulated Gas Pressure
1. Attach a manometer (or a dry gas pressure
gauge) to heater jacket (see Figure 34).
2. Open both columns on the manometer.
3. Use shutoff valve, on outside of heater jacket, to
shut off all gas supply to the heater.
4. Remove the 1/8 inch (3.2 mm) NPT test plug on
the outlet side of the manifold, and replace it
with the 1/8 inch (3.2 mm) NPT fitting from the
manometer kit, (see Figure 34).
5. Attach one end of the manometer hose to the
fitting on the manifold and the other end to the
manometer.
6. Turn on gas supply to the heater, and set the
temperature control high enough to call for heat.
7. Turn toggle switch to ON. This should activate
the main burners.
8. The manometer reading should be 4 inches
(102mm) W.C. for natural gas and 9 inches
(229mm) W.C. for propane gas.
9. Turn the toggle switch to OFF.
10. Shut the system down following the instructions
found on the inside of the heater.
11. Disconnect the manometer tubing from the
manifold and replace the 1/8 inch (3.2 mm) NPT
fitting with the original plug.
5.2 Electrical Troubleshooting
This section describes procedures for checking
the electrical power and control components of the
heater. Read all of these procedures before starting
repairs.
Problems with heaters not firing are usually
caused by something reducing water flow through the
heater, causing the protective switches in the heater
system to shut down the heater.
The following tools are required for proper
service and problem diagnosis of the heater and
heating system.
1. Gas pressure test kit with range from 0 to 14
inches (0 to 356 mm) W.C.
Figure 35. Testing the transformer.
2. Electric meter(s) with the following ranges:
a. 0 to 500 volts VAC
b. 0 to 2000 ohms ( )
c. 0 to 20 microamps (mA)
d. 0 to 50 millivolts (mV)
3. A pressure gauge and a thermometer with proper
ranges for heater operation.
5.2.1 Heater Does Not Come On
Important: Disconnect power to the heater or
pull the RED wire off the transformer secondary
before removing or replacing any component or wire
connection.
WARNING
If power is not disconnected, jumpering gas valve or
accidental grounding of the wire harness, or
component terminals to the heater frame or jacket
could cause the ignition control fuse to blow or may
cause the heater to fire, resulting in injury or
property damage.
1. Make sure the heater has been properly installed.
2. Make sure the pump is not airlocked, clogged or
otherwise inoperative.
3. Make sure the gas valve is on and there is gas
pressure in the line.
4. Check all electrical connections and wiring.