| b 08 | Pressure switch circuit open | • Blockage in intake or vent system. |
| | • Vent and/or intake system not constructed in accordance with Part VI |
| | • Blocked or leaking pressure switch tubing |
| | • Heat exchanger or burner blockage |
| | • Terminals exposed to high winds |
| | • Blockage in condensate trap above vent. |
| b 18 | MCBA supply sensor detected temperatures in excess of200°F | • Heating load at time of error was far below the minimum firing rate c boiler |
| | • Defective primary pump or no flow in primary loop (Piping Method |
| | • Control system miswired so that boiler operation is permitted when n are calling |
| b 19 | MCBA return sensor detected temperatures in excess of200°F | • See possible causes for “bl8” |
| | • Flow through boiler reversed |
| | • Sensor wiring reversed |
| b 24 | MCBA is reading a return sensor temperature higher than the supply sensor temperature. Condition must be present for at least 75s for this error code to appear. | • Flow through boiler reversed. Verify correct piping and pump orienta |
| | • No boiler water flow. Verify that system is purged of air and that appi valves are open. |
| | • Sensor wiring reversed. |
| | • Supply or return sensor defective. |
| b25 | Supply water temperature has risen too quickly | • See possible causes for “bl8” |
| | • Inadequate boiler water flow. Verify' that pump is operating and that pump and piping are sized per Part VIII of this manual |
| b26 | Boiler safety limit, or external limit wired across terminals 3&4, is open. | • See possible causes for “bl8” |
| | • Defective supply sensor. |
| b 30 | Temperature rise between supply and return is too high. | • Inadequate boiler water flow. Verify' that pump is operating and that pump and piping are sized per Part VIII of this manual |
| b 61 | Pressure switch circuit closed with fan off | • Blockage in pressure switch hose |
| | • Pressure switch wires shorted together |
| | • Defective pressure switch |
| | • Loose or miswired fan speed harness (if “b61” error code is observed while fan is running) |
| b65 | Fan is not achieving set point speed | • Loose or incorrect fan speed control connection |
| | • Defective fan |
| E 00 | A flame signal was present when there should be no flame. | • Defective gas valve make sure inlet pressure is below maximum on rating plate before replacing valve. |
| E 02 | Flame failure after 5 tries to restart | • No gas pressure |
| | • Gas pressure under minimum value shown on rating plate |
| | • Gas line not completely purged of air |
| | • Defective Electrode |
| | • Loose burner ground connection |
| | • Defective Ignition Cable |
| | • Defective gas valve (check for 24 VDC at harness during trial for ignition before replacing valve) |
| | • Air-fuel mixture out of adjustment consult factory |
| E 03 | Gas valve error | • Loose or defective gas valve harness. Check electrical connections. |
| | • Defective gas valve (check for 24 VDC at harness during trial for ignition before replacing valve) |
| E 04 | Power failure occurred after lockout | • Some other error on this list occurred and power to the boiler was then interrupted. Reset control and see if hard lockout reoccurs. |
| E 05, E 06, E 07, E 11 | Internal control failure | • Reset the control. If problem reoccurs, replace the MCBA. |
| E 12 | Low water cut-off circuit open | • If yellow light on LWCO is on, system is low on water |
| | • If neither yellow nor green light is on, check LWCO harness and check for 24VAC across AT140 transformer |
| E 13, E 14, E 15, E 16, E 17 | Internal control failure | • Reset the control. If problem reoccurs, replace the MCBA. |
| E 18 | MCBA supply sensor detected temperatures in excess of 200°F for an extended period of time | • See possible causes for “b18" error. Also, check safety limit for proper operation. |
| E 19 | MCBA return sensor detected temperatures in excess of 200°F for an extended period of time | • See possible causes for “b19“ error. |
| E 28 | Blower is not running when it should or fan speed signal not being detected by MCBA | • Loose connection in 120 VAC fan wiring |
| | • Loose or miswired fan speed harness |
| | • Defective fan |
| E 29 | Blower fan speed has not returned to zero rpm | • Miswired fan speed harness |
| | • Defective fan |
| E 31 | Shorted supply temperature sensor | • Shorted or miswired supply sensor wiring |
| | • Defective supply sensor |
| E 32 | Shorted return temperature sensor | • Shorted or miswired return sensor wiring |
| | • Defective return sensor |
| E 35 | Flue gas temperature sensor short circuit | • Shorted or miswired flue temp sensor wiring |
| | • Defective flue temp sensor |
| E 36 | Supply water temperature sensor circuit open | • Loose or miswired supply sensor wiring |
| | • Defective supply sensor |
| E 37 | Return water temperature sensor circuit open | • Loose or miswired return sensor wiring |
| | • Defective return sensor |
| E 40 | Flue gas temperature sensor circuit open | • Loose or miswired flue temp sensor wiring |
| | • Defective flue temp sensor |
| E 44 | Internal control failure | • Reset the control. If problem reoccurs, replace the MCBA. |
| E 52 | Flue gas temperature over 230°F | • Heat exchanger needs to be cleaned |
| | • Boiler over-fired |
| | • Air-fuel mixture out of adjustment consult factory |
| E 60 | Internal control failure | • Reset the control. If problem reoccurs, replace the MCBA. |
