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FlowMax · Combi boiler

E02 Safety (overheat) thermostat or air pressure switch tripped

High severity FlowMax condensing combi (FLOWMAX-90/120)

What the control is telling you

The heating safety thermostat has opened (trips at 203°F) or, per the 120 manual, the air pressure switch has opened. Note: the 120 diagnostics list also has a separate E14 for the air pressure switch, and the 90 user manual lists E02 as safety thermostat only.

Applies to: FLOWMAX-90, FLOWMAX-120

Likely causes

  • Safety thermostat faulty or out of calibration
  • Safety thermostat wire disconnected
  • Air pressure switch faulty
  • Combustion air intake or exhaust vent blocked
  • Air pressure switch wiring loose / intermittent

Test and repair steps

  1. Find out why the heat exchanger overheated before resetting (circulation, pump, air in the system, closed valves).
  2. Check the safety thermostat wiring and connections.
  3. Test the safety thermostat; replace it if it is faulty or out of calibration (trip point 203°F).
  4. Inspect the intake and exhaust vent pipes and terminals for blockage (snow, nests, debris) and clear them.
  5. Check the air pressure switch wiring and hoses; replace the switch if it does not operate.
  6. Reset with the ON/OFF switch and confirm normal operation.

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Source: FlowMax FLOWMAX-120 Instruction Manual, 6.10 Troubleshooting table, p.66; FlowMax FLOWMAX-120 Instruction Manual, 6.11 Diagnostics error code list, p.67; FlowMax FLOWMAX-90 User Manual, Diagnostics - Error codes, p.8-9. Summarized in our own words; check the original manual for your model.

Homeowner looking at this code? See what it means for you and when to call a technician.

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.