Rinnai / Grundfos GTK03U Pump Kit — Smart Recirculation with Circ-Logic™
The GTK03U Pump Kit enables hot water recirculation using Rinnai’s Circ-Logic™ technology on tankless water heaters lacking built-in pumps. It includes a Grundfos 15-55 pump with an internal check valve, prewired conduit, and flange kit, allowing you to enjoy “instant hot water” without needing a dedicated return line.
Key Features & Benefits
- Enables Circ-Logic™ recirculation on compatible Rinnai models (VC, KB, Sensei)
- Includes Grundfos 15-55 pump with internal check valve
- Pre-wired conduit with 4A fuse for plug-in setup
- Flange / union kit for ¾″ piping connections
- Stainless-steel pump housing resists corrosion
- Reduces water waste — hot water delivered faster to fixtures
Applications
- Tankless water heaters without built-in recirculation pumps
- Retrofit installations using Circ-Logic™ mode
- Crossover loops or dedicated return loops where allowed
- Homes seeking to reduce wait time and wasted water
Specifications
| Model / SKU |
GTK03U Pump Kit |
| Pump Type |
Grundfos 15-55 with check valve |
| Flow Rating |
20 GPM (nominal) |
| Head Rating |
17 ft (5 m) |
| Max Liquid Temp |
150 °F (65 °C) |
| Max System Pressure |
145 PSI |
| Voltage / Frequency |
115 V, 60 Hz |
| Max Current |
0.75 A |
| Connection Size |
¾″ flange / union |
| Weight (pump + flange kit) |
~8.6 lbs (4 kg) |
| Included Kit Items |
Pump + internal check valve, 6 ft BX conduit prewired (with 4A fuse), Circ-Logic manual |
Common Questions
Q: Which Rinnai heaters support this kit?
A: Compatible with many VC, KB, and Sensei series models using Circ-Logic mode.
Q: Do I need a return line?
A: The kit is meant for use in systems with dedicated return lines where possible. Some configurations may be limited by code or manufacturer rules.
Q: Can it be used outdoors?
A: The pump is intended for indoor installation per manufacturer guidelines.
Q: Is installation difficult?
A: An authorized technician should handle gas, water, and electrical connections for safe and code-compliant installation.
With the GTK03U pump kit, your tankless setup gains responsive hot water delivery, better efficiency, and compatibility with Rinnai’s Circ-Logic platform.
If you are installing a GTK03U Kit on one of the following tankless water heater models, follow the instructions in Section 2 in the install Manual:
RU199i/e
RU180i/e
RU160i/e
RU130i/e
CU199i/e
CU160i/e
If you are installing a GTK03U Kit on one of the following models, follow the instructions in Section 3 in the install Manual:
RLX94i
RL75i/e (VC models)
RL94i/e (VC models)
RU98i/RUC98i and RU98e (KB models)
RU80i/RUC80i and RU80e (KB models)
Housing Material Stainless Steel with Check Valve
Flow Range 20 GPM
Head Range 17 Ft (5 m)
Max Liquid Temperature 150° F (65° C)
Maximum System Pressure 145 PSI
Input Voltage 115 V
Frequency 60 Hz
Max Amperage 0.75 A
Connection Size 3/4” Flange
Weight (Pump/Flange Kit Combined ) 8.6 lbs. (4 kg)
Pipe Length
Equivalent pipe length using Grundfos GTK03 pump at
120°F (49° C) = Up to 200 Ft (61 m) (3/4” piping).
Equivalent pipe length includes supply piping, return piping and
fittings. The installer/contractor/engineer must calculate the total equivalent
pipe length of the piping system
