LAARS Mighty Therm LO-NOx VW (Sizes 250/400) - Installation, Operation and Maintenance Instructions - Manual (Page 24)

LAARS Heating Systems Page 24
5.2 Electrical Troubleshooting
WARNING
Electricity can cause property damage, injury, or
loss of life. All troubleshooting and servicing must
be done by a qualified hot water heater technician.
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.
2. Electric meter(s) with the following ranges:
a. 0 to 500 volts VAC
b. 0 to 2000 ohms (
W)
c. 0 to 20 microamps (
mA)
3. Tube cleaning kit with a reamer, stainless steel
brush, speed handle, and handle extensions.
4. 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 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 an electrical shock hazard and could
cause the ignition control fuse to blow or may cause
the heater to fire, resulting in property damage,
injury or loss of life.
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.
Finding a loose connection or a charred wire can
save a lot of time and money.
5. Check the fuse inside the twist-lock fuse holder.
If it is burned, replace it with a 2-amp fuse (Part
No. E0084400). If there is a short, the cause of
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 shutoff valve outside the heater
and follow the lighting instructions in Figures 27
and 28 to turn on the heater.
7. With the main burners firing, the manometer
reading should be between 6 and 10.5 inches
(152 and 267 mm) W.C.
Suggested
Manometer
Position
Main
Shutoff Valve
(Field
Supplied)
Manifold
Pressure Tap
Figure 36. Gas Manifold Pressure Test.
5.1.2 Checking the Manifold
Regulated Gas Pressure
1. Attach a manometer (or a dry gas pressure gauge)
to heater jacket (see Figure 36).
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 gas valve, and replace it
with the 1/8 inch (3.2 mm) NPT fitting from the
manometer kit.
5. Attach one end of the manometer hose to the
fitting on the gas valve and the other end to the
manometer.
6. Turn on gas supply to the heater, and follow the
lighting instructions in Figures 27 and 28 to turn
on the heater.
7. With the main burner firing, the manometer
reading should be 4 inches (102mm) W.C. for
natural gas.
8. Turn the toggle switch to OFF.
9. Shut the system down following the shutdown
instructions in Figures 27 and 28.
11. Disconnect the manometer tubing from the gas
valve and replace the 1/8 inch (3.2 mm) NPT
fitting with the original plug.
OUT OF
PRODUCTION