HVACopediaFlowMax · Combi boiler
E12 DHW storage tank (cylinder) sensor fault
What the control is telling you
Only on units set up to heat an indirect storage tank (parameter 1 = 01 or 02). The tank sensor reads out of range; sensor is 10 kOhm at 25°C. Lead may be up to 8 m long.
Applies to: FLOWMAX-90, FLOWMAX-120
Likely causes
- Tank sensor faulty or wrong type
- Tank sensor wire disconnected or wet
Test and repair steps
- Confirm the unit is configured for a storage tank (parameter 1) - if no tank is installed, the setting may be wrong.
- Check the tank sensor lead and connection at the board; maximum lead length is 8 m.
- Measure the sensor about 10 kOhm at 25°C (77°F).
- Replace the sensor if faulty or incorrect.
- Restart and confirm the code clears.
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
- E02 Safety (overheat) thermostat or air pressure switch tripped
- E03 Flue gas thermostat / exhaust thermofuse tripped
- E05 Heating (supply) sensor fault
- E06 Domestic hot water (DHW) sensor fault
- E14 Air pressure switch tripped
- E16 Fan (blower) fault
- E22 Parameter programming request
- E35 Flame detection fault (false flame)
Save it for the next call
Star this code in the HVACopedia app and keep the whole library on your phone for jobs with no signal.
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. 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.