20 Twinning fault

What the control is telling you

Twinning was detected and then lost in the same power cycle.

Applies to: 802P/80MDP (802PA050-150); R95P (R95PA040-115)

Likely causes

• TWIN wire broken or disconnected
• Controls not identical (different part numbers)
• 24 VAC transformers out of phase
• TWIN setting wrong on a single furnace

Test and repair steps

1. Check the wire between the TWIN terminals of both controls and the C and W connections (802P: also W2).
2. Confirm both IFCs have the same part number (R95P manual: UT 1194-200 board).
3. Check transformers are in phase (out of phase makes flame LED dim); both furnaces must be on the same power phase.
4. For a single (non-twinned) furnace make sure TWIN is set to single / nothing connected.
5. R95P see twinning wiring diagrams Fig. 43 (1-stage) and Fig. 44 (2-stage).

Settings for these units

Clearance to combustibles (all models) · R95P

Same values for R95PA040 through 115.

Column order read from a rotated drawing header - confirm on the furnace clearance label.

Reduced clearance to combustibles, upflow/horizontal (Fig. 4) · Rheem/Ruud 802P / 80MDP 80% two-stage furnace (UT 1028-928 IFC)

Note 2: right side may be 0 in. with type B vent.

Note 3: vent clearance may be 1 in. with type B vent.

Models that show this code

11 models in Rheem/Ruud 802P / 80MDP 80% two-stage furnace (UT 1028-928 IFC), R95P

Other codes on the same units

• 10 One-hour lockout
• 11 Failed ignition
• 12 Low flame sense
• 13 Flame lost
• 14 Unexpected flame
• 22 Main limit open
• 26 Line and neutral reversed
• 33 Rollout switch (MRLC) open