To increase water pressure for a Rinnai tankless water heater, check for clogs, ensure proper pipe sizing, and consider a pressure booster pump if needed.
Low water pressure in your Rinnai tankless water heater can be frustrating. Weak showers and slow-filling sinks are common complaints. Fortunately, there are several ways to boost your system’s performance.
Check Your Water Filter First
The most common cause of low pressure is a clogged filter. Rinnai units have an inlet water filter that traps sediment before it enters the heater. Over time, this filter can become blocked.
Steps to Clean the Filter:
- Turn off the water supply to the unit
- Locate the filter housing (refer to your manual)
- Remove and rinse the filter under running water
- Reinstall the filter and turn water back on
For heavily clogged filters, soak in vinegar overnight. Replace filters annually for best performance.
Inspect Your Pipes
Old or corroded pipes can restrict water flow. Check for:
- Mineral buildup in pipes
- Kinked or crushed water lines
- Improper pipe sizing (should be at least 3/4″)
Consider replacing old galvanized pipes with copper or PEX. This can dramatically improve flow. For help with pipe sizing, see our guide on proper duct and pipe sizing.
Adjust the Flow Restrictor
Some Rinnai models have an adjustable flow restrictor. This device helps maintain proper temperature but can limit pressure.
| Model Series | Flow Restrictor Location |
|---|---|
| RU | Inlet water connection |
| RUR | Behind front panel |
Consult your manual before making adjustments. Turning the restrictor counterclockwise typically increases flow.
Check Your Home’s Main Pressure
Your tankless unit can’t create pressure – it only works with what your home provides. Test your home’s static water pressure:
- Purchase a pressure gauge (under $10 at hardware stores)
- Attach to an outdoor faucet or washing machine connection
- Turn on the faucet fully and read the pressure
Ideal pressure is 50-70 psi. Below 40 psi, consider installing a pressure booster pump.
Consider a Recirculation System
Rinnai’s Smart-Circ™ recirculation system provides instant hot water while maintaining pressure. This system:
- Reduces wait time for hot water
- Maintains consistent pressure
- Can be controlled via smartphone
According to Rinnai’s official site, their recirculation technology learns your usage patterns for optimal performance.
Descale Your Heat Exchanger
Mineral buildup inside the heat exchanger can restrict flow. Descaling should be done annually in hard water areas.
Use only Rinnai-approved descaling solutions. The process involves:
- Flushing the unit with vinegar solution
- Running the solution through the heat exchanger
- Rinsing thoroughly with clean water
For severe scaling, professional service may be needed. The ENERGY STAR program recommends regular maintenance to preserve efficiency.
Upgrade Your Water Supply
If all else fails, consider these upgrades:
Pressure Booster Pump
Installs on your main water line to increase pressure throughout the house.
Larger Water Lines
Upgrading from 1/2″ to 3/4″ pipes can significantly improve flow.
Whole-House Filter
Reduces sediment before it reaches your tankless unit.
Remember that Rinnai recommends professional installation for any major modifications. Their PRO Network technicians are specially trained on tankless systems.
