Are isolation valves required on a tankless water heater?

Many manufacturers recommend or require serviceability provisions, and some jurisdictions require them by code on new installs. Regardless of requirement, the unit is not practically flushable without them.

How much does it cost to add isolation valves to an existing tankless heater?

The valve kit itself is modest, and a plumber's installation typically runs one to two hours of labor. It is a one-time cost that converts every future flush into a DIY job.

How do I know if my tankless heater already has isolation valves?

Look at the two water lines directly below the unit. Isolation valve kits show a pair of lever-handle valves, usually with blue and red handles, each with a smaller capped port sticking out. Bare pipes with no levers and no capped ports mean no kit.

Can I install isolation valves myself?

A confident DIYer comfortable sweating copper or working with the unit's fittings can, but the connections carry full house pressure at the appliance, so most owners are better served by a plumber's hour.

Isolation Valves on Tankless Water Heaters: What They Are For

Page last reviewed: August 2026 · Reviewed by Harold R. Bennett, retired home inspector

Isolation valves on a tankless water heater are the pair of shutoff valves with built-in service ports installed on the hot and cold lines at the unit, and they exist for one purpose: making the heater serviceable. Without them, the descaling flush that determines the unit’s lifespan is somewhere between impractical and impossible. This reference covers what the kit is, how to spot one, and what to do if your installer skipped it.

What the kit actually is

A standard isolation valve kit contains three functions in two assemblies. The isolation function: quarter-turn ball valves on the cold inlet (blue handle) and hot outlet (red handle) that disconnect the heater from house plumbing without shutting water to the rest of the home. The service function: on each valve body, a smaller port with a threaded cap and its own little valve, sized for standard 3/4 inch hose connections. And usually a pressure relief function: a relief valve on the hot side, required by many codes at the appliance.

The service ports are the whole point. They are where the flush pump’s hoses connect, letting descaling solution circulate through the heat exchanger while the isolation valves keep it out of your drinking water piping.

Why some units do not have them

Cost and corner-cutting. The kit adds parts and installation time, and builder-grade or bargain installations sometimes omit it, leaving bare connections. The unit works fine on day one either way, which is how the omission survives inspection by owners. The bill arrives years later as a choked heat exchanger that was never flushed because flushing was never practical, the failure arc described in HARD WATER AND SCALE.

The two-minute audit: look below the unit for the lever handles and capped ports. If you see plain pipe, put the retrofit on the list ahead of everything else in the maintenance schedule, because every other water-side task depends on it.

The retrofit

Adding a kit to an existing installation is routine plumbing: shut the house water, cut in or re-fit the connections at the unit, install the valve set, restore and check. A plumber does it in one to two hours, and it is a fair moment to have the tech do a first professional flush while connected. For DIYers, the job is within reach for anyone comfortable making pressurized connections at an appliance, with the usual caveat that a drip here drips onto an expensive machine.

Buying notes are short: full-port valves in a lead-free brass body, service ports with proper hose threads, and a hot-side relief valve if your local code wants one at the heater. Kits are widely available from plumbing suppliers and from the same maintenance-focused brands that sell flush equipment, Chromex among them.

What the valves make possible

With the kit in place, the unit becomes a serviceable appliance. The annual descaling becomes a bucket-and-pump job instead of a service call. The inlet filter screen becomes reachable behind its own shutoff. A failed component can be worked on without draining or shutting down the house. And winterizing a seasonal property, draining the exchanger against freezing, becomes a five-minute task. It is a modest set of brass that converts the most maintenance-sensitive appliance in the house from sealed to owned.

The bottom line

Isolation valves with service ports are the difference between a tankless heater you can maintain and one you can only watch age. Check for the levers and capped ports today; if they are missing, the retrofit is the single highest-leverage hour of plumbing labor the unit will ever receive.