Hatco Booster Heater Error Code: Error Light Flashing, Low Water
A flashing Error Indicator Light on a Hatco electric booster heater means the low-water cutoff probe is defective or the tank has a low-water error. Do not power the heater until the tank is full and the air is vented. If the light stays on after that, call a Hatco service agent.
High: the control protects the elements by stopping heat, and the heater should stay off until the water level is confirmed.
- Code
- Error Indicator Light flashing
- Maker
- Hatco
- Equipment
- Booster heaters
- Applies to
- Electric booster heaters, Imperial, Compact, Mini-Compact series
What does Hatco error indicator light flashing mean?
A Hatco booster heater keeps its heating elements covered with water. A low-water cutoff probe in the tank tells the control whether water is present, and the control cuts power to the elements when it is not. When the control sees a low-water error, or when the probe is defective, the Error Indicator Light flashes. The manual lists three causes: a defective probe, low water in the tank, and low-water cutoff contacts that do not close because the probe is fouled. The warning in the manual is firm. Never power the heater until the tank is full and the air is vented, because dry firing burns out the elements. The manual also gives a probe test: remove the probe wire and touch it to the tank. If the contacts close, the probe is fouled and has to be cleaned or replaced.
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 blinking
- Heater not heating the rinse water
- Light still flashing after the water supply is restored
Possible causes
Listed in Hatco's documentation
- Probe defective
- Low water in the tank
- Low water cutoff contacts do not close (probe fouled)
Other likely causes — what usually sits behind error indicator light flashing on this control. A technician confirms which one it is before any part is replaced.
- Mineral coating on the probe from hard water, which stops it sensing water
- Air trapped in the tank after a drain or service, so the probe sits in a pocket
- Supply to the heater shut off or throttled upstream, such as a closed valve on the booster line
Safe checks before calling for service
- Check that the water supply valve to the booster is open and that water is reaching the tank.
- Leave the heater switched off at the power disconnect until you are sure the tank is full and vented.
- If the light still flashes with water present, note it and call a Hatco service agent.
- For the service call, write down whether the heater was recently drained, any water supply work nearby, and the model series.
How a technician diagnoses error indicator light flashing
- Confirm the flashing pattern, then lock out and tag the supply before any tank work.
- Verify water supply and confirm the tank is full and air-vented.
- Following the manual's test, remove the probe wire and touch it to the tank to see whether the low-water cutoff contacts close.
- If the contacts close, clean or replace the fouled probe.
- Restore power only after the tank is verified full, and watch the first heat-up.
- The probe test happens at the tank of a heater wired to line voltage, so power has to be locked out and tested with a meter.
- Dry firing destroys elements quickly, so a wrong guess about the water level has a direct cost.
- Cleaning or replacing the probe and bleeding air from the tank means opening plumbing connections on a hot water vessel.
How error indicator light flashing differs from similar codes
A steadily lit Error Indicator Light is a different condition. It points to the high temperature limit, not the low-water cutoff.
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); Troubleshooting Guide (PDF pp.22-23)
- 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
Why is the light flashing and not steady?
On a Hatco booster the flashing light points to the low-water cutoff probe or low water. A steady light means the high limit tripped.
Can I turn it on to check?
No. The manual says never to power the heater until the tank is full and air is vented.
What if water is present and it still flashes?
The manual lists a defective or fouled probe as a cause, which a technician can test with the probe wire touched to the tank.
Need help with Hatco error indicator light flashing?
A technician confirms the cause on site and gives you the price in writing before any work starts.