State Water Heater E45 Error — What It Means
E45 on a State tankless water heater is an internal leak or water detection fault. The unit has found water where it should not be, typically at the leak sensor in the base of the cabinet, and has shut down as a safety measure. This is not an ignition or flame problem. It is a leak-protection shutdown.
In the field, technicians see this code after servicing (when residual water triggers the sensor), from a slow seep at the mixing valve area, or from a small leak at internal plumbing connections that allows water to collect in the bottom pan. Even a minor amount of water near the sensor will trip E45 and lock out the heater until the leak is repaired and the unit is thoroughly dried.
Before You Replace Anything
Homeowners sometimes replace the leak sensor itself, but the sensor is only reporting water that is actually present. Always inspect for the true leak source (mixing valve, fittings, or leftover service water) before replacing any sensor.
Common Causes
- Residual water after service (~35%) Water left in the cabinet from a recent valve replacement or maintenance drips onto the leak sensor and triggers E45 until the unit is completely dried.
- Mixing valve seep or leak (~30%) A slow leak from the mixing valve allows water to collect in the bottom of the chassis and activate the leak sensor.
- Internal plumbing connection leak (~20%) A loose or corroded fitting on the water manifold or nearby piping drips water into the base pan.
- Water intrusion from external source (~10%) Condensate, roof leak, or splash from nearby plumbing enters the cabinet and pools at the sensor.
- Faulty leak sensor reporting false positive (~5%) The sensor itself shorts or fails and reports water even when the cabinet is dry (rare, verify by thorough visual inspection first).
Quick Diagnosis
Answer these to narrow it down fast.
Has the unit been serviced or opened in the past week?
No: An active leak is present. Proceed to inspect the mixing valve and all internal fittings.
Can you see or feel any standing water in the bottom of the cabinet when you remove the access cover?
No: The sensor may have triggered from earlier moisture that has already dried, or the sensor itself is faulty. Attempt a reset after confirming the cabinet is bone-dry.
Does the code return immediately after you dry the unit and restore power?
No: The problem was transient moisture. Monitor for recurrence over the next few days.
Step-by-Step Fix
- Shut off electrical power to the water heater at the breaker or disconnect switch.
- Close the cold-water supply valve to stop any further water entry into the unit.
- Drain or relieve water from the heater by opening a hot tap downstream and the drain valve, so you can work safely.
- Remove the front access cover and inspect the bottom of the cabinet for standing water, wet spots, mineral trails, or drip marks near the leak sensor and lower components.
- Dry the unit completely using towels and shop rags. If you recently had service and no active leak is visible, let the cabinet air out for at least an hour.
- Identify the leak source if water is actively present. Check the mixing valve body and connections, internal manifold fittings, and nearby pipe joints for seepage.
- Repair or replace the leaking component. Tighten fittings, replace the mixing valve, or reseal connections as needed, then reassemble the unit.
- Restore the cold-water supply and electrical power, then monitor the heater during a hot-water draw to confirm the E45 code does not return and no new leaks appear.
Parts Often Needed
| Part | Notes |
|---|---|
| Mixing valve (State / A. O. Smith tankless) | Amazon | Most common component leak associated with Code 45; verify your model number before ordering. |
| Water leak detection sensor | Amazon | Replace only if the cabinet is dry and the code persists; sensor rarely fails on its own. |
When to Call a Pro
Call a licensed plumber or water-heater technician if you cannot locate the leak source, if the mixing valve or internal manifold needs replacement, or if the code returns after you have dried the unit and verified all visible fittings are tight. Tankless water heaters have high-pressure gas and water connections that require proper tools and permits in many jurisdictions. A pro will isolate the leak, replace the correct component, and test the unit under full operating pressure to confirm no recurrence. If your unit is still under warranty, professional installation of replacement parts is often required to preserve coverage.
Rough cost: A pro service call runs about $150-350 depending on leak source and part.