How should a drained tankless heater be restarted after power returns?

MGI’s recommendation: Have the refill and restart verified against the exact model before restoring operation. Power returning is only one part of getting a drained heater safely back in service.

If you smell gas, get everyone outside to a safe location. Do not use switches or phones inside. Call 911 and your gas supplier from safety. Do not approach the heater. Xcel Energy gas safety guidance Stay outside until the gas utility confirms it is safe to return. Utility gas-return guidance.

The Rinnai RSC manual has a separate sequence for resuming operation after draining. It checks the drain components and water flow before restoring power and gas in its specified order. This is conditional guidance for the listed RSC models, not a universal restart checklist. Rinnai RSC manual, draining and resuming operation

Tell the qualified provider exactly what was drained, who drained it, and which plugs, valves, or accessories were involved. If you do not know, say so. Give them the model label, any freeze exposure, and photographs taken from a safe position.

The restart needs to establish that the heater and connected piping are intact, all disturbed components are correctly restored, the unit is properly refilled, and any freeze damage or leak is addressed. Have the provider explain how these checks were made, rather than relying on “the faucet runs” as the entire clearance to restart.

If the heater or piping may be frozen, keep the unit out of operation until qualified assessment. A leak after thawing changes the job from a routine restart to an equipment and water-system repair. Do not apply a homemade thawing method or improvise electrical power.

If the power came back while the unit was still drained, tell the provider that too. Do not keep cycling it to see whether it recovers. A successful reset would not verify the refill or repair any damage.

After the approved restart, ask for a steady hot-water test and a leak check, with the findings recorded. Confirm who owns any separate plumbing or electrical work and whether the tankless appointment includes this model-specific restart.

Until then, plan around having no dependable hot water. The extra verification now is more useful than an avoidable second failure after the outage.