Keeprite HI

What does Keeprite HI mean?

The HI fault on the Keeprite PGD4/PGS4 packaged gas-electric unit indicates that the high gas pressure switch (HGPS) has tripped, cutting off the gas supply to the burners. The HGPS is a safety device that opens when gas manifold pressure exceeds the upper design limit, protecting the heat exchanger and burner assembly from a high-fire condition.

Symptoms

• Gas burners shut off unexpectedly during a heating call
• Unit displays HI on the diagnostic indicator
• No ignition on subsequent heat calls until the fault clears
• Possible smell of gas if the overpressure condition is severe

Common causes

• Gas supply pressure to the unit exceeds the allowable manifold pressure range
• Defective or failed gas pressure regulator not stepping pressure down correctly
• High gas pressure switch out of calibration, opening at pressures within normal range
• Wiring fault causing a false trip of the HGPS circuit
• Clogged or restricted gas valve orifice causing pressure buildup upstream

Diagnostic steps

1. 01

   Verify incoming gas supply pressure

   Connect a manometer to the inlet pressure tap on the gas valve and measure static and operating supply pressure. Supply pressure must be within the range specified on the unit rating plate, typically 5–14 in. w.c. for natural gas.

2. 02

   Check manifold gas pressure

   Measure the manifold (outlet) pressure at the gas valve outlet tap during a heat call. Compare the reading to the nameplate specification; adjust the gas valve regulator if pressure is out of range.

3. 03

   Test the high gas pressure switch

   With power off, disconnect the HGPS wiring and check switch continuity at rest. The switch should be closed (continuous) at atmospheric pressure. A switch that reads open at rest is failed and must be replaced.

4. 04

   Inspect wiring to the HGPS

   Check the wiring harness between the HGPS and the IGC for loose terminals, corrosion, or chafed insulation that could cause an intermittent open circuit.

5. 05

   Contact the gas utility if supply pressure is high

   If the supply pressure at the unit service cock is above the maximum rating, contact the gas utility to adjust the service regulator. Do not modify the utility regulator yourself.

When to call a professional

Gas pressure measurement and gas valve adjustment require a calibrated manometer and knowledge of local gas codes. If supply pressure is out of range, the gas utility must correct it. If the gas valve regulator is faulty or the HGPS needs replacement, engage a licensed HVAC or gas technician. Operating a gas appliance with incorrect manifold pressure creates combustion efficiency and safety hazards.