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Glow Brand · Boiler troubleshooting

Boiler pressure keeps dropping / FILL shows

Glow B85/B120/B160

What is going on

The system loses pressure and the display asks to fill.

Likely causes

  • System leak
  • Expansion tank precharge wrong or tank failed
  • Relief valve weeping
  • No automatic fill valve

Check in this order

  1. Fill to about 16 psi; the burner is blocked below 4 psi (Err 116) and immediately below 10 psi (Err 162).
  2. Check the expansion tank precharge matches system pressure and that the relief valve is not discharging.
  3. Look for leaks, including underground piping; consider an automatic fill valve where codes allow.
  4. If pressure on the external gauge is fine but the display still says FILL, clean or replace the pressure sensor.

Applies to: B85, B120, B160 (NG and LP)

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Source: Glow Brand B85/B120/B160 Installation & Operation Manual V20231025, 10.1 p.47, 12.2 p.64-65. Written in our own words; check the manual for your exact model.

For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.