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LAARS Mighty Therm2 MT2V (Sizes 200, 300, 400) - Install and Operating Manual User Manual

Page 33

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Mighty Therm

2

(200, 300, 400)

Page 33

SECTION 8.

Trouble Shooting

8.1 Resolving Lockouts

There are many causes of lockouts. The three

most common causes are: (1) inadequate gas supply,

(2) poor combustion, (3) ignitor failure.

1. Inadequate gas supply: Before proceeding, ensure

that the gas supply has not been shutoff or the LP

tank (LP boilers) is not empty. Then, restart the

boiler and observe the operational cycle. After

a 15-second fan pre-purge, the ignitor will heat

up for 40 seconds, and then the unit will light.

If it does not, check the gas supply pressure to

the appliance, after resetting the appliance and

attempting another start-up. The gas pressure to

the appliance must be above 5 in. w.c. (1.2 kPa)

throughout the entire start-up cycle. If it is not,

correct the supply problem (check gas valves or

supply piping). If the supply pressure is adequate,

consult the factory for assistance.

2. Poor Combustion: Poor combustion should

be suspected if there is a strong flue gas odor.

The odor may result from an improper gas/air

ratio (high or low O

2

or CO

2

). Mighty Therm2

appliances operate best with 45% excess air (8%

CO

2

on natural gas, 9.2% CO

2

on LP). Check the

CO

2

of the appliance and adjust if necessary.

3. Ignitor failure: If the boiler goes through a

normal start cycle but combustion does not

occur, ignitor failure should be suspected. Check

the ignitor by unplugging the ignitor plug and

measuring the ignitor resistance. It should be

50-80 ohms. If the resistance is not 50-80 ohms,

replace the ignitor. If the resistance is correct,

reset the boiler and check for 120 VAC at the

ignitor plug during the start cycle. If there is no

voltage, replace the faulty ignitor wire harness or

the ignition control.

8.2 Delayed Ignition — Possible Causes

A defective burner can cause a delayed ignition.

If the gas supply pressure is proper and the gas

valves are functioning properly, then burners should

be inspected. There should be no distortion or

perforations in the burners outside of the active burner

port area. Replace if indicated.

8.3 Short Cycling — Boiler

Boiler short cycling is caused when the load

on the boiler system swings rapidly causing frequent

cycling between call for heat and satisfied conditions.

This condition is greatly reduced on two stage

units. If short cycling is a problem, it may be due

to an oversized boiler, incorrect set points or a load

distribution problem. If desired temperature response

is not achievable without short cycling it may be

necessary to install a buffer tank in the system. Contact

your Laars representative to discuss possible remedies.

8.4 Short Cycling — Water Heater

Short cycling will generally occur only in

combination space heating and water heating

applications when the water heater is operating in the

space-heating mode. If the heating load drops below

the minimum input of the water heater for an extended

period, the water heater will have a tendency to short

cycle. If short cycling is frequently experienced,

regardless of the control’s attempt to limit it, the

heating load should be redistributed to control it.

If short cycling occurs in a water heater

application, it is probably caused by undersized

piping between the water heater and the storage tank

or by some other factor that restricts proper water

flow through the water heater. The cause should be

determined and corrected.

8.5 High Gas Consumption

Appliances operating with an improper air/

fuel ratio are very inefficient and consequently, have

very high gas consumption. Because efficiency is

high when the CO

2

is high (or O

2

is low), appliances

operating with low CO

2

or high O

2

(especially LP

appliances) consume more gas. Adjust the CO

2

or O

2

for optimum efficiency. If no combustion analyzing

equipment (CO

2

or O

2

) is available then a proper

adjustment of the air/fuel ratio (CO

2

or O

2

) cannot be

accomplished. The CO

2

should be 8% at high fire for

natural gas and 9.2% at high fire for LP. To check the

CO

2

, first verify that the supply gas pressure is within

5 to 13 in. w.c. (1.2 to 3.2 kPa). With the Mighty

Therm2 running with all stages firing, set the air box

pressure to 1.8 in. w.c. (0.42 kPa) (as a starting point),

by adjusting the air shutter(s) at the intake of the

fan(s). Check the CO

2

, and adjust the air shutters if

further adjustment to the CO

2

is needed.

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