9 High-heat pressure switch or relay did not close or reopened

What the control is telling you

Two-stage models: the high-heat pressure switch (or the relay that drives high heat) did not close, or opened again.

Applies to: KeepRite (F/G)9MXT two-stage 95% furnace

Likely causes

• Faulty control relay
• Gas valve miswired
• Any of the venting/drain/pressure switch causes listed for code 3

Test and repair steps

1. Check the gas valve wiring against the diagram.
2. Go through the code 3 checks for vent, drain, tubing and inducer.
3. Check the high-heat switch with a manometer during high-fire.
4. If wiring and switch are fine, the board relay is suspect - replace the control.

Settings for these units

• Filter size by casing width · KeepRite (F/G)96VTN Two-Stage Variable-Speed Furnace

Models that show this code

8 models in KeepRite (F/G)9MXT Two-Stage Furnace

Other codes on the same units

• 5 Flame sensed with gas valve off
• 6 Flame not proved during ignition trial
• 6+1 Ignition lockout after 4 failed tries
• 7 Limit circuit lockout
• 8 Gas heating lockout - manual reset needed
• 10 Line voltage polarity reversed
• LED off Status LED dark - no power to the control or blown 3 A fuse
• LED steady ON Status LED on solid - control lockout (resets after 1 hour)