A033_F: Over Temperature Switch (Rollout) Open
Status
This is a critical fault. The furnace will not operate in gas heat modes but all other modes (e.g. cooling) should function.
Description
The Manually Reset Limit Control (M.R.L.C.) is also known by the name "Rollout Limit". There can be several on any given furnace. When one or more of these limits open, they must be manually pushed back to the closed position(hence the name; Manually Reset) to force the acknowledgement of a critical fault. This fault will occur when flames have rolled out of the normal area in the heat exchanger and into the burner compartment. This fault should rarely (if ever) be seen in the field and indicates a very serious problem that must be repaired before furnace operation can continue.
Expected Operation
When the MRLC (Manually Reset Limit Control) circuit has been opened, the IBM (Indoor Blower Motor) is energized at maximum heating speed. The gas valve circuit is de-energized (if it was energized) and the IDM (Induced Draft Motor) is energized at high speed. Response to thermostat cooling calls will take place as normal with IBM energizing at the higher of the two blower speeds (high heat or cool) when a call for cooling is also present. When the fault is cleared, the IDM will remain energized for a 20 second post-purge and the IBM will remain energized for the user-selected blower off-delay period.
Cause
1. Insufficient venting through either the inlet or exhaust.
2. Loose or faulty wiring.
3. Unstable flame pattern.
Solution
1. Check that the pressure switch(es) have not been welded closed or bypassed. Check that the inducer is operating at the proper rpm. Insure that the venting does not exceed the maximum specified lengths. Check for obstructions in combustion venting. Check that all gaskets between the inducer and center panel / heat exchanger are properly installed and sealed.
2. Check wiring and connections. Replace and/or repair as necessary.
3. Check that all burner assembly components are properly installed. Check that all seals between the burner and blower compartments are tight. Insure that the door seals are in place and that the burner door is properly installed and does not leak.Check to make sure that the heat exchanger has not been damaged; i.e.: crushed tubes, breached collector box and etc.
