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-   -   355 MAV Furnace (http://www.diychatroom.com/f17/355-mav-furnace-160215/)

Bubbles17 10-15-2012 05:52 PM

355 MAV Furnace
 
I have a Bryant 355 MAV furnace & is is throeing Error code 33 Limit or flame roll out switch is open. What do I need to do to fix the problem?

Marty S. 10-15-2012 06:14 PM

Roll out switches trip when the heat exchanger has a crack or the flue is plugged up. Heat exchanger inspection is beyond most home owners ability. You can make sure the flue is clear though simply by looking through it.

Limits trip because it has gotten too hot from lack of air flow. Most common causes are dirty filters of a failed blower motor.

Bubbles17 10-15-2012 06:37 PM

Where is the flue located at? Any other options you can think of?

techpappy 10-15-2012 06:51 PM

start with easiest ... by replacing the air filter..it may be plugged up with dust etc. Also could have dirty A Coil if there is Air Conditioning..The A Coil is in the supply air plenum ...usually above furnace.

The flue is the pipe coming out of the top of the furnace and isn't that easy to see sometimes. If gas fired then niot likely blocked however chimney could be blocked by birds nest or dead birds etc. Can check by removing "clean out at base and using a mirror or flashlight to see if any signs of blockage

Bubbles17 10-16-2012 10:46 AM

Why would the fan run all they time also?

techpappy 10-16-2012 03:33 PM

which fan..I'll assume you mean the induced draft fan on the front of the unit..it will run in start up mode waiting for the air switch to prove air flow prior to pilot and main ignition..but I don't think it will run indefinitely

check air proving switch by removing sensing line and blowing/sucking on line ...should hear clicking of switch..also clean out orifices where the line connects to fan and switch..use extended paper clip or similar to clean out..let us know what happens

Bubbles17 10-16-2012 05:35 PM

Its the blower fan that wont shut off?

HVACTECH96 10-16-2012 05:38 PM

Call your local bryant dealer.You are describing what sounds like a plugged secondary heat exchanger, causing burner box to get hot and makes limit trip.The repair is replacement of secondary and is covered under a warranty program by carrier.

HVACTECH96 10-16-2012 05:41 PM

Also ,Im guessing you are using LP gas, and if so you should have primary and secondary HE replaced along with burners.

Bubbles17 10-16-2012 06:12 PM

No I am using natural gas. The furnace was working fine till now. I even took the thermsitat off the wall & the blower motor to disperce the air is still running & it shows a fault code of 33. It wont even try to lite. Anything else I can also try?

HVACTECH96 10-16-2012 08:34 PM

burners are inclosed in a box.on outside of box on the right hand side is a limit with two red wires and a small button in middle.If u push button and it clicks, it has tripped do to too high temp in burner box.If furnace comes on and fires , look in sight glass and you will probable see flames not being pulled into heat exchanger properly and rolling out.If you see this and limit trips again, dont reset it because it is dangerous to keep resetting limit which defeats its purpose to tell u somethings not right.Call a dealer to correct problem.

beenthere 10-17-2012 05:28 AM

Probably have a tripped high limit that isn't closing. Check it. When its tripped, the blower will run all the time.

techpappy 10-17-2012 09:19 AM

doesn't a tripped hi limit close to energize the fan? Then open to stop the fan once the heat exchanger has cooled off, therefore wouldn't that be a hi limit that isn't opening/is stuck closed? AND if so does that also prevent start up therefore, there is another set of contacts that open and cut off the limit/start up circuit? Therefore it is a hi limit tat won't close. I think I just answered my own question but, hopefully this helps the OP,

First part of fix is to replace the Hi Limit.

beenthere 10-17-2012 02:58 PM

No, a high limit opens, so it can shut off the burner. has no direct control over the blower. The blower runs when the high limit opens because the board is programmed/wired to close the fan relay when the high limit opens.

techpappy 10-17-2012 03:15 PM

Thanks. Beenthere.....that's what I said..almost...only, differently:laughing:


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