Checking Temperature Sensors - Weil-McLain Ultra Manual

Gas-fired water boilers – series 3

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Installation and start-up manual (113 pages)

Manual addendum (28 pages)

Instruction manual supplement (12 pages)

Table of Contents

gas

fired water boiler

Troubleshooting

U-Control fault indications

The U-Control provides information for both automatic reset

conditions and manual reset conditions. See Figure 87, page 68

for information available on the U-Control display.

2. Figure 94 lists conditions that will cause the control to display a

constant red screen. The boiler will automatically restart if the

condition self-corrects or the technician uses the U-Control's

manual reset screens to reset.

Figure 94

Conditions that will cause an automatic reset problem notification (screen constant red, with exclamation mark symbol)

Message displayed

Display fault

Automatic reset limit open

Supply water temperature high

Return water temperature high (heat

exchanger input)

Return water temperature greater than

supply water temperature

Supply water rising too fast

Supply greater than return by 58 °F

Temperature sensors

Flue temperature high

LWCO fault

Checking temperature sensors

The boiler temperature sensors (flue, outdoor, return

water and supply water) are all resistance-type de-

vices.

The table at right shows the correct value for the sensor

at various temperatures.

Use the resistance values at 32°F, 60°F, 70°F and 212°F

to measure the sensor resistance at known temperatures

(ice point, room temperature and sea level boiling

point). For ice point and boiling point, insert the sensor

in water at that temperature. Use an ohmmeter to read

resistance value.

To check whether the control module is correctly sensing

temperature, you can use a resistance decade box. Con-

nect the decade box temporarily in place of a sensor and

read the corresponding temperature on the U-Control

display. The temperature should be close to the value

corresponding to the input resistance.

Part number 550-100-066/0608

— Boiler Manual

(continued)

Condition causing automatic reset

Display communications out for 30 seconds

Set if auto reset limit open

Set if the supply water temperature is higher than 200 °F

Set if the return water temperature is higher than 200 °F

Set if heat exchanger inlet temperature is higher than the heat exchanger outlet

temperature + 10 °F

Set if supply water temperature rises faster than 2 °F per second

Set if current heat exchanger outlet temperature is greater than the heat exchanger

inlet temperature + 58 °F

Supply sensor open or shorted

Return sensor open or shorted

Set if flue sensor not balanced (more than10 °F difference between sensors)

Set if heat exchanger outlet sensor not balanced (more than10 °F difference

between sensors)

Set if flue temperature over 210 °F

Set if LWCO open goes to manual reset lockout if open more than 1 second

3. Figure 95 shows the screen behavior during an auto-

matic or manual reset condition. The table below the

display illustration lists manual reset conditions and

how to reset from them.

Make sure to determine the causes of

outages. Do not leave the boiler operating

without a complete diagnosis.

Reset action

Resets automatically when communication is

re-established

Reset after auto reset is closed for 2.5 minutes