HVACopediaFlowMax · Combi boiler
E02 Safety (overheat) thermostat or air pressure switch tripped
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
- Find out why the heat exchanger overheated before resetting (circulation, pump, air in the system, closed valves).
- Check the safety thermostat wiring and connections.
- Test the safety thermostat; replace it if it is faulty or out of calibration (trip point 203°F).
- Inspect the intake and exhaust vent pipes and terminals for blockage (snow, nests, debris) and clear them.
- Check the air pressure switch wiring and hoses; replace the switch if it does not operate.
- Reset with the ON/OFF switch and confirm normal operation.
Settings for these units
Installation clearances · FlowMax condensing combi (FLOWMAX-90/120)
| Location | Service clearance (in) | To combustibles |
|---|---|---|
| X (side) | 0 | 0 in |
| Y (side) | 0 | 0 in |
| L | 16 | - |
| H | 24 | - |
| A (above) | 12 | 0 in from jacket top |
| B (below) | 12 | - |
| Front | - | 0 in |
| Rear | - | 0 in |
Wall-mount on a flat, solid vertical wall that can carry the weight.
Letters follow fig. 1 of the manual; L and H are the clearance zone in front/around the unit as drawn.
Hot water scald risk by temperature · FlowMax condensing combi (FLOWMAX-90/120)
| Temperature setting | Time to 2nd/3rd degree burn (adult skin) |
|---|---|
| Over 170°F | Nearly instantaneous |
| 160°F | About 1/2 second |
| 150°F | About 1-1/2 seconds |
| 140°F | Less than 5 seconds |
| 130°F | About 30 seconds |
| 120°F or less | More than 5 minutes |
120°F lowers scald risk; children, elderly and disabled people burn faster.
Fit a tempering (mixing) valve if water is stored or set hotter, e.g. with parameter 1 = 03 (up to 160°F).
Models that show this code
2 models in FlowMax condensing combi (FLOWMAX-90/120)
Other codes on the same units
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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.