Mighty Therm VW - PW Volume Water Heaters
Page 29
Thermocouple
Thermocouple
Adapter
Gas Valve
Millivolt
Meter
Pilot
Figure 41. Testing the pilot thermocouple.
5B-17. Heater Will Not Shut Off
1.
If the heater stays on with the brown wire on the
gas valve disconnected, replace the gas valve (see
Section 4B).
WARNING
Never attempt to repair the gas valve. Such
attempts will void the warranty, and could lead to
dangerous results.
2.
Check electrical components for loose wires.
Disconnect one of the lead wires on the gas
valve. If the heater goes off, the wiring could be
at fault. Repair or replace as necessary.
5B-18. On-Off Main Burner Cycling
The main burners cycling on and off can be
caused by:
1.
Poor wind conditions on an outdoor installation.
2.
Pilot components out of position.
3.
Low gas pressure causing an improper pilot
flame.
The pilot flame may appear to be all right until
the main burners come on, then the pilot flame shrinks.
An undersized gas supply line may cause this.
5B-19. Testing the Terminal Strip/External
Controls
The terminal strip has been included so the heater
can be operated by various external controls not
provided by Laars. Determine whether or not an
external control is open by checking for voltage at
each terminal. If there is voltage at one terminal and
not the other, examine the external control. It may
require service or replacement.
2.
If everything appears all right, measure flame
sensing current by connecting a direct current
(DC) microamp meter between terminal No. 12
and the GND (BURNER) terminal on the ignition
control (see Figure 42).
NOTE: Separate the microamp meter leads from
each other and clear the heater chassis for most of their
length to properly perform this test.
3.
When the pilot lights, the microamp meter should
read 1.5 microamps or more with or without the
main burners firing. A smaller current could be
caused by poor pilot flame, the position of the
pilot electrode, or bad cable and connectors.
4.
If the pilot flame and sensor electrode are all
right, but there is no main burner ignition, clip
one lead from a volt meter between the yellow
wire terminal on the transformer and the brown
wire terminal on the gas valve.
5.
If the voltmeter reads between 20 to 28VAC, but
the main burners do not fire, replace the gas
valve (see Section 4B).
5B-16. Testing for Burner Ignition
(for standing pilot)
If the pilot flame and pilot thermocouple
generator are all right, but there is no main burner
ignition:
1.
Clip one lead of a volt meter between the yellow
wire on the transformer and the brown wire
terminal on the gas valve.
2.
If the volt meter reads between 20 to 28VAC, but
the main burners do not fire, replace the gas
valve (see Section 4B).
Figure 42. Flame sensing current.
