HVACopediaGlow Brand · Boiler
Loc 15 High limit exceeded (203 F / 95 C)
What the control is telling you
The supply water went past the high temperature limit.
Applies to: B85, B120, B160 (NG and LP)
Likely causes
- Primary, CH or DHW pump not running
- Not enough flow through the heat exchanger
- High limit switch contact or continuity problem
- Supply or return sensor reading wrong
- System pressure below 10 psi
- Heat exchanger micro-fuse open (HX went above 336 F / 169 C)
- Tank sensor or aquastat wiring problem
- Secondary pump not running or turning the wrong way
Test and repair steps
- Confirm the primary, CH and DHW pumps run.
- Confirm there is enough flow through the boiler (minimum flow table).
- Check the high limit switch contact and continuity.
- Compare supply and return sensor readings while running.
- Make sure system pressure is above 10 psi.
- Check the heat exchanger micro-fuse for continuity. If it is open the HX overheated past 336 F and must be replaced.
- If an indirect tank is used, check its sensor/aquastat wiring and the secondary pump direction.
Settings for these units
Maintenance intervals · Glow B85/B120/B160
| Item | When |
|---|---|
| Annual inspection by a technician | Every year (warranty) |
| Relief valve try-lever test | Annually |
| LWCO test | Annually |
| Condensate trap clean | Annually (14.3) |
| Heat exchanger combustion-side wash | Annually or when combustion drifts (14.4) |
| Burner door silicone gasket | Replace if damaged or after 2 years |
| Service reminder | 2.203 on, interval 2.204 (default 1000 days) |
Operating pressure should sit 5 psi under the relief valve rating (max 25 psig on a 30 psi valve); water never above 180 F.
Models that show this code
3 models in Glow B85/B120/B160
Other codes on the same units
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Source: Glow Brand B85/B120/B160 Installation & Operation Manual V20231025, Table 12.1 p.62. Summarized in our own words; check the original manual for your model.
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