Hi Everyone,

I have a strange intermittent problem with my Bryant 350MAV furnace that has arisen in the last couple of months, since the weather started to cool here in Los Angeles.

I usually turn off the thermostat at night when I go to bed, then manually turn on the heat in the morning when I get up. As per usual, I've done that this season, and my heater fires and runs as long as I ask it to each morning without trouble.

However, when the temperature drops again in the evenings and it either tries to come on again manually, or I turn the heat setting back up, one of two things happen: either it simply refuses to fire at all, or it fires up normally, the fan blows hot air for two or three minutes, and then it shuts off.

The following morning it will start up again normally, but no matter how many times I try it throughout the evening, it will not start.

Today, the same process occurred. When I tried to turn it on again a few minutes ago, the unit ran for a couple of minutes and then shut down. I examined the LEDs on the control center, and they were all dark. None were flashing, so there was no error code being reported.

This has happened every day for the past six weeks or more. The unit works and operates normally each morning, but refuses to start each evening.

I would really appreciate any advice or suggestions about how to investigate this problem. Does the lack of a flashing error code mean nothing is wrong with the furnace, or is the fact that they're dark itself a problem?

Thanks very much,

Raphael
Los Angeles

Normally the LED is on steady. Blinking indicates a fault - see service label inside front panel. No LED indicates power supply lost.

Normally the LED is on steady. Blinking indicates a fault - see service label inside front panel. No LED indicates power supply lost.

Hi KC13,

Before turning on the unit to test it a short while ago, I looked at the LEDs, and they were blank then as well.

Then I turned the unit on, it shut off after blowing for a couple of minutes, and I looked at the LEDs a second time. They remained blank.

In other words, they were blank both before and after I turned the thermostat to heat and the unit ran for a few minutes.

It's odd to me that unlit LEDs indicate no power, but the unit still turned on for a few moments. Does that suggest anything to you?

Thanks very much,

Raphael.

You mentioned LED's (plural)... the 350 circuit board has only one. Are there more than one? If so, re-check model number... 352? 355?

You mentioned LED's (plural)...the 350 circuit board has only one. Are there more than one? If so, re-check model number...352? 355?

I think there were four LEDs, so I think you're right that I made a mistake with the model number (the manual for my unit is for the 340MAV, 350MAV, and 355MAV, as you probably guessed). The front of the unit calls itself the Plus 90i.

I'll climb back up in the attic when I get home later today, and recheck the model.

Thanks for helping me out.

The style 90i is either a 398B, 320, or 355MAV. The LED display is a little different on these boards, and there will be more than one. These will only indicate when the unit is operating in low fire (green), high fire (yellow), or faulting (alternating yellow and green). They do not remain lighted to indicate power status. If they are not displaying a fault code, the thermostat and/or thermostat wiring may be the problem. The service label inside the front panel describes a process for retrieving fault codes stored in the processor memory. Checking this may shed more light on the subject.

The style 90i is either a 398B, 320, or 355MAV. The LED display is a little different on these boards, and there will be more than one. These will only indicate when the unit is operating in low fire (green), high fire (yellow), or faulting (alternating yellow and green). They do not remain lighted to indicate power status. If they are not displaying a fault code, the thermostat and/or thermostat wiring may be the problem. The service label inside the front panel describes a process for retrieving fault codes stored in the processor memory. Checking this may shed more light on the subject.

I wasn't able to test the unit until today because of Christmas.

It is indeed the 355MAV.

The error code was first "12" and then "44", which has to do with restricted airflow.

I have an electrostatic filter and I was fooled on first inspection into thinking it was not particularly dirty, when in fact it was.

I thoroughly cleaned the filter and it is now running fine. As a note, when the furnace throws those error codes, it retries in low speed, and I was really not getting much hot air blowing during the days when it was running after throwing the errors.

I really appreciate your helpful and quick replies!