Bradford White Error Code 20: High Limit Overheat Switch Open (Infiniti Tankless)

What the code means

Bradford White's Infiniti GS (RTGS199) and GR (RTGR199) installation and operation manuals define code 20 as "High Limit Overheat Switch – Closed is Normal, Open is Fault." The high limit overheat switch is a safety switch that opens when it gets too hot, and the control treats an open switch as a fault. It is a hard lock, which Bradford White defines as a lockout that requires a manual reset (a soft lock resets itself when the issue subsides). The error flashes on the display as Er followed by the number. Two related codes are worth knowing: 16 means the operating temperature sensor or hot water (DHW) sensor read water hotter than 199°F (93°C), and 43 means the separate burner overheat switch is open. Code 20 on the Infiniti GS and GR is not the same as the codes on Bradford White tank water heaters, which use their own code lists, and older Infiniti K-series units use a different letter-number system.

Likely causes

• The heat exchanger overheated and tripped the high limit overheat switch, for example from too little water flow or scale build-up (Bradford White lists flushing the heat exchanger for the related hot-water-temperature code 60)
• A loose or poor connection at the high limit overheat switch
• A failed high limit overheat switch that no longer closes, even when cool

Safe DIY checks

1. Press the Power button to clear the code, as Bradford White's table instructs, and see whether the heater runs normally.
2. If the heater has been running hard, let it cool before resetting; the switch must close again before the heater can restart.
3. Clean the cold water inlet filter. Bradford White's maintenance steps include removing it, cleaning out residue and making sure the cap is tightened securely.
4. If you have hard water and the heater hasn't been flushed recently, plan a heat exchanger flush. Bradford White recommends a straight white vinegar solution (or a commercial descaler at the maker's dilution) circulated for at least 1 hour at about 4 gallons per minute through the isolation valves, but says flushing is a complicated job that should be done by an authorized technician or licensed professional, and that improper maintenance can void the warranty.
5. Don't keep resetting the heater if code 20 returns; the switch is a safety device telling you something is overheating.

Parts that commonly fix it

Always match the part number to your exact model.

Related codes

• 10 Bradford White Tankless Water Heater 10
• E012 / 012 / 012E Navien Tankless Water Heater E012 / 012 / 012E
• E109 / 109 / 109E Navien Tankless Water Heater E109 / 109 / 109E
• 11 Noritz Tankless Water Heater 11
• 12 Noritz Tankless Water Heater 12

All Bradford White codes →

Sources

1. Bradford White Infiniti GS Series Installation and Operation Instructions 238-54627-00 (RTGS199): error code 20 High Limit Overheat Switch, closed is normal, open is fault, Hard Lock, press Power to clear, check connections and continuity at room temperature; codes 16 and 43; flushing procedure and flushing alarm
2. Bradford White Infiniti GR Series Installation and Operation Instructions 238-54628-00 (RTGR199): same code 20 entry, hard lock vs soft lock definitions, code 60 flush step, inlet filter cleaning, vinegar flush at 4 GPM for 1 hour by an authorized technician
3. Bradford White Quick Service Guide 238-55958-00 (eF Series ICON HD tank models): tank-model code list, which does not include code 20; Technical Support 800-334-3393