Two accessories make a tankless water heater far easier to live with: an isolation valve kit, which lets you shut off water and connect flush hoses without draining the house, and a flush kit, which circulates descaler through the heat exchanger once a year. These five kits are the best we found for installing and maintaining a tankless heater.
We compared parts included, materials, pump size and compatibility using manufacturer specifications and owner feedback. For scale filters see the best tankless water heater replacement filter guide, and for low-upkeep heaters see the best tankless water heater easy maintenance guide; our Editorial Policy explains how we choose. Gas connections must be made by a licensed installer.
Top 3 Tankless Water Heater Accessories Kits
CMI 3/4″ IPS Complete Tankless Water Heater Valve Kit
- Valves + hoses
- Gas hose
- Tape
Green Expert Tankless Water Heater Flushing Kit with 1/4HP Pump
- 1/4HP pump
- 1800 GPH
- Locking lid
Rheem RTG20220AB Webstone Tankless Water Heater Service Valve Kit
- Webstone
- Relief valve
- Clean brass
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Tankless Water Heater Accessories Kits Compared
| # | Product | Key Features | |
|---|---|---|---|
| 1 |  CMI 3/4″ IPS Complete Tankless Water Heater Valve Kit |
| Check Latest Price |
| 2 |  Rheem RTG20220AB Webstone Tankless Water Heater Service Valve Kit |
| Check Latest Price |
| 3 |  Matsui 3/4″ Isolation Valve Kit with Pressure Relief Valve |
| Check Latest Price |
| 4 |  Green Expert Tankless Water Heater Flushing Kit with 1/4HP Pump |
| Check Latest Price |
| 5 |  Chromex Tankless Water Heater Flush Kit with Descaling Solution |
| Check Latest Price |
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1. CMI 3/4″ IPS Complete Tankless Water Heater Valve Kit
Best Complete Kit
- Includes valve set, 2 brass nipples and Teflon tape
- 18″ gas line hose and two 18″ water hoses
- Clean brass for low-lead rules
- Pressure relief valve
- 3/4″ only
- Indoor style
- Size: 3/4″ IPS
- Material: clean brass
- Brand: CMI
CMI bundles nearly every part an install needs.
It saves a trip to the supply store.
Who the CMI complete kit fits best
New installs.
Who should skip the CMI complete kit
Existing valves.
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2. Rheem RTG20220AB Webstone Tankless Water Heater Service Valve Kit
Best for Rheem
- Webstone hot and cold service valves
- Relief valve included
- Clean brass for California low-lead codes
- Fits all Rheem gas tankless models
- Valves only
- Rheem-focused
- Type: service valve kit
- Material: clean brass
- Model: RTG20220AB
Rheem’s kit combines several valves and connections in one part.
It simplifies future flushing.
Who the Rheem Webstone valve kit fits best
Rheem owners.
Who should skip the Rheem Webstone valve kit
Those wanting hoses.
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3. Matsui 3/4″ Isolation Valve Kit with Pressure Relief Valve
Best Build
- Heavy-duty forged brass
- Color-coded hot and cold handles
- 100% leak tested
- Complies with NSF/ANSI 61
- FNPT only
- Hoses not included
- Size: 3/4″
- Thread: FNPT x FNPT
- Brand: Matsui
Matsui’s compact valves fit recess boxes and pipe covers.
The hex lever prevents misuse.
Who the Matsui valve kit fits best
Neat installs.
Who should skip the Matsui valve kit
PEX-only needs.
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4. Green Expert Tankless Water Heater Flushing Kit with 1/4HP Pump
Best Flush Kit
- 1/4HP pump, 1800 GPH
- 3-gallon pail with locking lid
- Two 6-ft PVC hoses
- Wrench and quick-start guide
- Descaler not included
- Needs service valves
- Pump: 1/4HP, 1800 GPH
- Hoses: 2 x 6 ft
- Model: 203648
Green Expert’s stronger pump moves solution through the exchanger well.
Pair it with isolation valves.
Who the Green Expert flush kit fits best
Yearly DIY flushing.
Who should skip the Green Expert flush kit
No valve ports.
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5. Chromex Tankless Water Heater Flush Kit with Descaling Solution
Best All-in-One Flush
- Includes NSF-certified descaling solution
- 1/6HP pump
- 5-gallon bucket with lid
- Works with most tankless brands
- Smaller pump
- Solution runs out
- Pump: 1/6HP
- Bucket: 5 gallons
- Brand: Chromex
Chromex includes descaler, so you can flush right away.
It works with most brands.
Who the Chromex flush kit fits best
First-time flushers.
Who should skip the Chromex flush kit
Pros wanting more flow.
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How to Use These Kits
- Install isolation valves during setup.
- Turn off power or gas before flushing.
- Circulate descaler as the manual directs.
- Clean the inlet screen after flushing.
Frequently Asked Questions
What accessories does a tankless water heater need?
An isolation valve kit and a flush kit.
Do isolation valves come with the heater?
Usually not.
How long does flushing take?
Follow the manual, often about an hour.
Can I use vinegar?
Some makers allow it; check the manual.
Final Verdict: Best Tankless Water Heater Accessories Kit
The CMI complete kit is the best tankless water heater accessories kit for new installs. The Green Expert kit is the best flush kit, and the Rheem Webstone kit is best for Rheem owners.
Complete kit: CMI 3/4″ IPS Complete Tankless Water Heater Valve Kit Check Latest Price
Flush kit: Green Expert Tankless Water Heater Flushing Kit with 1/4HP Pump Check Latest Price
Rheem: Rheem RTG20220AB Webstone Tankless Water Heater Service Valve Kit Check Latest Price
The right kit makes maintenance a one-hour job.
Looking for something else? Browse all of our Water Heaters guides and the wider Heating & Cooling section.
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