What causes Rheem Tankless Water Heater 45?

Water reaching the leak detector at the bottom of the cabinet from a leaking internal water connection, valve or component (Rheem says to have a technician find and repair the source). A leak elsewhere in the heater's water circuit, such as the pump on recirculation models, that drips down inside the cabinet. A loose, damaged or wet connection at the water leakage detector itself (the service manual's diagnostic step is to check the detector connections).

How do I fix Rheem Tankless Water Heater 45?

Write down the code, then follow Rheem's steps: turn power off to the water heater. Valve the heater off to isolate it from the plumbing system. Close the water valves on the heater's cold inlet and hot outlet piping. Look around and under the heater for water and put a towel or pan down to protect the floor while you wait for service. If you see water spraying or a lot of water, shut off the home's main water supply. Don't just power-cycle the heater to get hot water back. Rheem's remedy for Er:45 is to find and repair the leak, not to clear the code. If the heater is gas, don't open the sealed parts of the unit or move gas lines yourself. If you smell gas, leave the house and call your gas utility from outside.

When should I call a pro for Rheem Tankless Water Heater 45?

Call a qualified service technician, as Rheem's error table directs. Tell them the code, the model number and whether the heater has recirculation. The technician opens the cabinet, traces where the water is coming from and repairs or replaces the leaking part. They check the water leakage detector connections at the main circuit board, since a bad connection or a wet detector can keep the code active. Once the leak is fixed and the detector is dry, they restore water and power and confirm the heater runs without the code returning.

Code: 45🚿 Rheem Tankless Water Heater

Rheem Tankless Error Code 45 (Er:45): Water Leak Detected (Meaning, Causes, Fixes)

Q: What does Rheem Tankless Water Heater 45 mean?

Er:45 on a Rheem condensing tankless water heater means its water leak detector has sensed water inside the cabinet. Rheem's error table calls it Water Leak, and its remedy is not a reset: turn off power to the heater, valve it off from the plumbing, and call a qualified service technician to find and repair the source of the leak. This code appears on Rheem's condensing models that show codes as Er:xx, such as the RTGH-RH10DV / RH11DV series and the ECOH200DVRHLN. Rheem's RTGH-RH10DV / RTGH-RH10DVLP / RTGH-RH11DV service manual lists Er:45 as Water Leak in its error code table. Its components chapter explains the part behind it: a water leakage detector, connected to the main circuit board, monitors for water leakage, and if it detects water the water heater closes its water supply valve. The service manual's only diagnostic step for the detector itself is to check its connections. The ECOH200DVRHLN Use and Care Manual (AP18733) has the same Er:45 Water Leak row with the same remedy. Unlike most codes in those tables, Rheem does not tell you to press the Power button to clear Er:45. Instead it says to turn power off to the water heater, valve the heater off to isolate it from the system, and have a qualified service technician diagnose and repair the source of the leak. Rheem's other tankless lines that show plain two-digit codes (for example the high and super high efficiency models in troubleshooting manual AP21822) have no code 45 in their error lists, so check which display your heater has.

Reviewed 2026-10-23 · Based on 4 manufacturer & service sources

What the code means

Rheem's RTGH-RH10DV / RTGH-RH10DVLP / RTGH-RH11DV service manual lists Er:45 as Water Leak in its error code table. Its components chapter explains the part behind it: a water leakage detector, connected to the main circuit board, monitors for water leakage, and if it detects water the water heater closes its water supply valve. The service manual's only diagnostic step for the detector itself is to check its connections. The ECOH200DVRHLN Use and Care Manual (AP18733) has the same Er:45 Water Leak row with the same remedy. Unlike most codes in those tables, Rheem does not tell you to press the Power button to clear Er:45. Instead it says to turn power off to the water heater, valve the heater off to isolate it from the system, and have a qualified service technician diagnose and repair the source of the leak. Rheem's other tankless lines that show plain two-digit codes (for example the high and super high efficiency models in troubleshooting manual AP21822) have no code 45 in their error lists, so check which display your heater has.

Likely causes

Water reaching the leak detector at the bottom of the cabinet from a leaking internal water connection, valve or component (Rheem says to have a technician find and repair the source)
A leak elsewhere in the heater's water circuit, such as the pump on recirculation models, that drips down inside the cabinet
A loose, damaged or wet connection at the water leakage detector itself (the service manual's diagnostic step is to check the detector connections)

Safe DIY checks

⚠ Before you start

Unplug the appliance (or switch off its breaker) and shut off the water supply valves before removing panels or disconnecting hoses. Keep towels handy for residual water.

Write down the code, then follow Rheem's steps: turn power off to the water heater.
Valve the heater off to isolate it from the plumbing system. Close the water valves on the heater's cold inlet and hot outlet piping.
Look around and under the heater for water and put a towel or pan down to protect the floor while you wait for service. If you see water spraying or a lot of water, shut off the home's main water supply.
Don't just power-cycle the heater to get hot water back. Rheem's remedy for Er:45 is to find and repair the leak, not to clear the code.
If the heater is gas, don't open the sealed parts of the unit or move gas lines yourself. If you smell gas, leave the house and call your gas utility from outside.

🛠 When to call a pro

Call a qualified service technician, as Rheem's error table directs. Tell them the code, the model number and whether the heater has recirculation.
The technician opens the cabinet, traces where the water is coming from and repairs or replaces the leaking part.
They check the water leakage detector connections at the main circuit board, since a bad connection or a wet detector can keep the code active.
Once the leak is fixed and the detector is dry, they restore water and power and confirm the heater runs without the code returning.

Parts that commonly fix it

Always match the part number to your exact model.

⚙

Water leak detector alarm

Optional extra sensor for the floor near the heater. It only alerts you; it doesn't fix the leak inside the unit.

Search eBay →

⚙

Water heater drain pan (sized for your heater)

Catches drips under a wall-hung tankless heater while you wait for repair, where installation allows.

Search eBay →

⚙

Combustible gas leak detector

For peace of mind around a gas water heater. Any real gas smell means leave and call the gas company.

Search eBay →

Sources

Last reviewed 2026-10-23. Always confirm against the manual for your exact model number.

Rheem Tankless Error Code 45 (Er:45): Water Leak Detected (Meaning, Causes, Fixes)

What the code means

Likely causes

Safe DIY checks

🛠 When to call a pro

Parts that commonly fix it

Water leak detector alarm

Water heater drain pan (sized for your heater)

Combustible gas leak detector

Related codes

Sources