Bradford-White Corp BMT2V Manual De Usuario

Page 35

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

). Brute Deluxe 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.

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.

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 

or stage controlled multiple boiler systems which can 

change heat input to better match the load. If short 

cycling is a problem, it may be due to an oversized 

boiler, improper control strategy, incorrect set points or 

a load distribution problem. If the set points are correct 

and the system design, controls scheme, etc. are fixed, 

the temperature differentials may be increased to 

reduce short cycling. If desired temperature response 

is not achievable without short cycling it may be 

necessary to install a buffer tank in the system. Contact 

your Bradford White representative to discuss possible 

remedies. 

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. 

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 Brute Deluxe 

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.