Hatco Booster Heater Error Code: Error Light Solid, High Limit
A steadily lit Error Indicator Light on a Hatco booster heater means the high temperature limit safety switch tripped because the unit overheated. Switch the Power I/O switch off, let the unit cool and switch it back on. If it will not reset or keeps tripping, call a Hatco service agent.
High: the heater stops heating until the limit is reset, and repeat trips mean something is wrong.
- Code
- Error Indicator Light solid
- Maker
- Hatco
- Equipment
- Booster heaters
- Applies to
- Electric booster heaters, Imperial, Compact, Mini-Compact series
What does Hatco error indicator light solid mean?
The high temperature limit is a safety switch that opens when the heater gets hotter than it should. When it trips, the Error Indicator Light, marked with a reset icon beside the Power I/O switch, stays lit steadily. The manual says the limit is reset with the Power I/O (on/off) switch. The sequence is to switch Power I/O off, or turn off power at the disconnect, let the unit cool, and then switch it back on. The manual lists three causes: the high temperature limit tripped, the high limit switch tripped or defective, and over-current fuses blown or a breaker tripped. The last one matters because the unit can stop heating from a protective device in the supply even when the high limit is healthy. A single trip after a hot spell or a flow problem can be reset by the operator. A limit that cannot be reset, or one that trips again, is a sign that something is causing the overheating.
Affected models and control systems
The manual covers Hatco electric booster water heaters in the Imperial, Compact and Mini-Compact series.
Code numbers and their meaning can change between control generations. We match the full model and control before acting on a code.
What you may notice
- Error Indicator Light on steadily
- Heater not heating after the light came on
- Booster not delivering hot rinse water
- Light returns soon after a reset
Possible causes
Listed in Hatco's documentation
- High temperature limit tripped
- High limit switch tripped or defective
- Over-current fuses blown or breaker tripped
Other likely causes — what usually sits behind error indicator light solid on this control. A technician confirms which one it is before any part is replaced.
- Water flow through the heater stopped or very low, so heat built up with nothing to carry it away
- Scale insulating the elements and driving the tank temperature up
- Thermostat that no longer shuts the elements off at the set temperature
Safe checks before calling for service
- Switch the Power I/O switch off and, if needed, turn off power at the disconnect.
- Let the unit cool completely before switching back on, as the manual directs.
- Switch Power I/O on and watch whether the light goes out and the heater starts.
- If the light comes back or the limit will not reset, stop resetting it and call a Hatco service agent.
- For the service call, note how many times the light has come on and what the water flow was like.
How a technician diagnoses error indicator light solid
- Read the light and confirm the high limit state after the unit has cooled.
- Check the supply breaker and the over-current fuses with a meter for continuity.
- Verify water flow through the heater and look for blockage.
- Test the high limit switch for continuity and compare the tank temperature with the thermostat setting.
- Check elements and the thermostat for the cause of the overheating.
- Replace the limit switch or thermostat only after the test shows it is the cause.
- Fuses, the breaker and the limit switch sit in an enclosure carrying line voltage that must be locked out before testing.
- A limit that trips repeatedly means a cause such as no flow or a stuck thermostat that has to be measured on the heater itself.
- Replacing a safety limit with the wrong part removes the protection it exists to provide.
How error indicator light solid differs from similar codes
A flashing Error Indicator Light on the same heater points instead to the low-water cutoff probe.
Technical reference
- Document
- Electric Booster Water Heaters, Imperial, Compact, and Mini-Compact Series, Installation and Operating Manual
- Edition
- P/N 07.04.111.00 (c) 2025
- Models / control
- Electric booster heaters, Imperial, Compact, Mini-Compact series
- Section
- Controls (PDF p.19); Maintenance: High Temperature Limit Safety Switch; Troubleshooting Guide
- Checked
- October 2026
We use the maker's document to read the code and do not reproduce it. Always confirm the complete model and control before applying these steps.
Related Hatco booster heater error codes
How do I reset it?
The manual says to use the Power I/O switch: turn it off, let the unit cool, then turn it back on.
Is it always the high limit?
Not always. The manual also lists blown over-current fuses or a tripped breaker as causes.
What if it keeps tripping?
The manual says to contact a Hatco service agent if the high limit cannot be reset or keeps tripping.
Need help with Hatco error indicator light solid?
A technician confirms the cause on site and gives you the price in writing before any work starts.