E14 = overheat / high-temperature lockout. The heat exchanger reached its temperature limit. Critical to diagnose immediately — sustained overheating destroys the heat exchanger ($1,500-2,500 replacement).
Why this matters urgently
Don\'t repeatedly reset E14. Each reset trial without addressing the root cause stresses the heat exchanger further. Diagnose first.
Diagnostic sequence
1. Heat exchanger scale (most common)
Scale buildup on the inside of the heat exchanger tubes insulates from water flow. Combustion gases heat the tube walls; water can\'t carry the heat away fast enough; temperature climbs past the limit.
- How to verify: when was the last descaling? If over 1 year ago in hard water, this is almost certainly the cause
- Solution: descale immediately. See descaling guide
2. Low flow rate
- Restricted flow doesn\'t carry heat away from the heat exchanger
- Clogged inlet filter, partially-closed shutoff, low-flow aerator
- Verify flow rate at unit inlet (bucket-and-stopwatch test)
3. Heat exchanger temperature sensor failure
- Sensor reads incorrectly high; control trips overheat lockout even when temp is normal
- NTC sensor test required
- Less common than scale
4. Combustion air restriction
- Blocked intake causes incomplete combustion; CO climbs; temperature may also climb
- Inspect intake termination
5. Gas valve trim drift
- If recent service didn\'t verify combustion analysis, trim may be off
- Lean combustion = higher heat exchanger temperatures
- Requires combustion analyzer to diagnose properly
The descaling solution
Most E14 events resolve with thorough descaling:
- Power off; gas off
- Close inlet/outlet shutoffs
- Connect descaling pump via service ports
- Circulate vinegar or descaler 60 minutes (longer for E14-triggering scale)
- Flush thoroughly
- Restore power and gas; test
If E14 returns after descaling, the scale was beyond what descaling can dissolve. Heat exchanger replacement or sensor diagnosis required.
Prevention
- Annual descaling in any hard water
- Whole-home softener in >10 gpg water (Westinghouse warranty requires softener at >7 gpg)
- Inlet filter cleaning every 6 months
- Periodic flow rate verification
Reset
- Wait 30+ minutes for heat exchanger to cool fully
- Descale before attempting reset
- Press Reset on control display
- If E14 returns within 1-2 uses = root cause not resolved; call tech support
Bottom line
E14 = scale. Descale immediately. Repeated E14 events damage the heat exchanger. Annual descaling prevents most E14 events. Hard water installs without softeners are at highest risk.