Xylem McDonnell & Miller GUARD DOG 750-MT-120, Instruction Manual, Page: 7 / 8

STEP 5 - Testing and Diagnostic Procedures
Series 750 LWCO with Green Power On LED and Red Low Water LED
Start-Up
turn on the electric power to the boiler.
a. Before filling the system,
1. Upon initial power up, Green and Red lights flash
2. Green and Red lights turn "ON". The burner remains "OFF".
b. Now fill the boiler with water.
Auto reset units:
1. When water touches the probe, the Green light will remain "ON".
2. The Red light will turn "OFF" and the burner will turn "ON" as
long as there is water on the probe.
Manual reset units:
(When water returns to the probe, nothing will happen until the manual reset button is depressed.)
1. After depressing manual reset button, the Green and Red lights will flash simultaneously 4 times.
2. Then the Green light will turn "ON" and the Red light will turn "OFF".
3. The burner will turn "ON" as long as there is water on the probe.
Manually Testing Control
c. Slowly drain the boiler of water.
Manual reset units:
1. When the water drops off the probe, the Green light will remain "ON".
2. The Red light starts flashing and the burner will turn "OFF", if water is off the probe.
If water below probe, Red LED turns "ON" and burner turns "OFF".
Auto reset units:
1. Green LED remains "ON".
2. Red LED turns "ON".
Testing Control Using "Test Button"
d. Depressing the test button with "water on probe"
(Must depress and hold test button to activate test cycle.)
1. Green stays "ON", Red flash twice and turns "ON".
2. The burner will turn "OFF".
(Release test button, if water is still on probe.)
3. The Green light remains "ON".
4. Then Red light will turn "OFF".
5. The burner will turn "ON" as long as there is water on the probe.
(Must depress and hold test button for 30 sec. to activate test cycle, Red LED will flash Green
1. Red LED turns "ON" and Green LED stays "ON" after test cycle is activated.
2. The burner will turn "OFF".
(Release test button. You must depress the manual reset button to unlock the low water cut-off.)
3. Then the Green light stays "ON" and the Red light will turn "OFF" after Red and Green lights
4. The burner will turn "ON" as long as there is water on the probe.
CSD-1 Compliance
On manual Reset units, if the control is in a low water condition (water off probe) when there is an
interruption of power, the control will remain in a low water condition when power is restored. The
reset button will need to be pressed when the water level is restored to a level above the probe.
If water returns to probe during 30 sec. Red LED will turn "OFF" and burner turns "ON".
LED "ON".)
Auto reset units:
Manual reset units:
7
flash simultaneously 4 times.
7
Auto reset units:
simultaneously 4 times.
Manual reset units:
1. Upon initial power up, Green and Red lights flash simultaneously
2. Green turns "ON" and Red light turns "ON" after flashing
continuously for another 30 seconds. The burner remains "OFF".
4 times.