5 blinks Twinning fault (optional)

What the control is telling you

Green STATUS LED blinks 5 times: twinned furnaces are not communicating/set up correctly. The 1028-928 board's "OK" LED also flashes when twinning is set up wrong.

Applies to: Rheem (-)GRC upflow and (-)GTC downflow/horizontal 90 Plus condensing gas furnaces (UT Electronic Controls 1012-925 / 1028-928 and Invensys ICC-H1MC7-01 IFC); Rheem 90RJ and 90TJ 90 Plus condensing gas furnaces (UT Electronic Controls 1012-925 or Invensys ICC-H1MC7-01 IFC, hot surface ignition)

Likely causes

• TWIN jumper/switch not set on both boards
• Missing or loose wire between the TWIN terminals
• 24 VAC transformers out of phase
• Boards of different part numbers
• Single furnace with TWIN not set to the single (OFF) position

Test and repair steps

1. For twinned units, set both IFCs to TWIN and verify the wire between the TWIN terminals.
2. Make sure the two transformers are in phase (if out of phase the flame LED will look dim); both furnaces must be on the same power phase.
3. Confirm both IFCs have the same part number - only twin furnaces with identical control boards.
4. For a non-twinned furnace, set TWIN to the single (OFF) position.
5. If all is correct, check the IFC.

Settings for these units

• Filter sizes (Table 12) · Rheem 90RJ/90TJ 90 Plus
• Minimum clearance to combustibles · Rheem 90RJ/90TJ 90 Plus
• Filter sizes (Table 9) · Rheem (-)GRC/(-)GTC 90 Plus
• Minimum clearance to combustibles · Rheem (-)GRC/(-)GTC 90 Plus