plumbing troubleshooting
Install tankless water heater
Common symptoms: converting to tankless; tankless install planning; replacing tank with tankless; endless hot water upgrade
Stop and call a pro if:
- gas-line sizing and pressure
- Category III stainless or PVC venting and termination clearances
- condensate acidity (neutralizer required for condensing units)
- dedicated electrical circuit
- permit and inspection requirement
- CO risk on improperly vented gas units
Step-by-step diagnostic flow
Step 1
Which scenario best describes your project?
The scope of a tankless install varies enormously. A whole-home gas conversion is a major job; replacing a small electric point-of-use unit with the same is a screwdriver job.
Step 2
Is the replacement unit the same voltage and amperage as the old one, fed from an existing dedicated circuit that's already correctly sized for the new unit?
Read both data plates. If amperage goes up at all, the circuit, breaker, and wire gauge may all need upsizing — that's electrician work.
Step 3
Is the new unit installing in the same location, with the same water connections and same shutoff valves?
Possible outcomes
Hire a licensed plumber — whole-home gas tankless is not a DIY project
high confidenceA whole-home gas tankless typically demands 150–200k BTU/hr — 4–5x a gas tank — which usually means upsizing the gas line from the meter to the unit, confirming meter and regulator capacity, installing Category III stainless or PVC venting per the model's spec with strict termination clearances, adding a condensate drain with neutralizer for condensing units, a dedicated 120V circuit, and a sediment trap. Each item has code consequences and CO/fire risk if wrong.
- Get 2–3 quotes from licensed plumbers who install your target brand
- Ask each quote to spec out: gas-line upsize calc, vent material + termination location, condensate drain + neutralizer, dedicated electrical, water-side isolation valves for descaling, and permit
- Confirm your gas meter and service can supply the added BTU load — the plumber should check with the utility if marginal
- Plan for the larger upfront cost vs. a tank; tankless wins on lifetime and capacity, not first-day price
- Get a water-hardness reading — hard water shortens tankless heat-exchanger life without annual descaling
- Photos of current heater, gas meter, panel, and proposed install location
- Distance from gas meter to install location
- Water hardness if known
- Peak hot-water demand (simultaneous fixtures)
Hire a licensed plumber + electrician — whole-home electric tankless is huge electrical load
high confidenceWhole-home electric tankless units typically need 80–150A at 240V — often 2–3 dedicated double-pole breakers and very heavy gauge wire. Most existing 200A panels can't accommodate this without a load calc, and many homes need a service upgrade. This is electrician territory before it's plumber territory.
- Have an electrician do a load calculation on your panel — many homes won't support whole-home electric tankless without a service upgrade
- If the panel supports it, get a plumber + electrician to scope the install jointly
- Compare lifetime cost vs. heat-pump tank — heat pump often wins on operating cost in mixed climates with major rebates available
- Pull permits for both plumbing and electrical work
- Photo of panel with cover off (by an electrician)
- Current main service amperage
- Photos of current heater and proposed location
- Peak simultaneous fixture demand
Major project — full design work needed before quotes
high confidenceGoing from electric tank to gas tankless requires a new gas line from the meter, all the venting and condensate infrastructure above, AND removing or repurposing the existing electric circuit. This is a multi-trade project that needs design, not just installation.
- Hire a licensed plumber for a paid site assessment and design
- Compare against the simpler alternative: stay electric and install a heat-pump water heater (often substantial rebates and no gas-line work)
- If proceeding with gas: budget for plumber, gas fitter (often the same person), and possibly utility service upgrade
- Pull all required permits — plumbing, gas, electrical
- Photos of current install, panel, and proposed location
- Distance to gas meter
- Whether you've already had a utility consult
Hire a licensed plumber — new install needs design
high confidenceAn install at a new location requires choosing the spot for vent clearances, gas/electrical access, water supply runs, and condensate drainage — these decisions affect performance and code compliance for the life of the unit.
- Hire a licensed plumber for site assessment
- Decide between gas and electric based on existing utilities and demand
- Pull permits for plumbing, electrical, and (gas) mechanical / gas
- Photos of proposed location with measurements
- Photos of nearby gas line / panel / water supply
- What fixtures the unit will serve
Get an electrician to size the circuit, then swap
medium confidenceIf the new point-of-use unit's electrical spec differs from the old one, the breaker and wire may need upsizing — that's panel work, not a DIY plumbing swap.
- Have an electrician confirm or upgrade the circuit, breaker, and wire gauge for the new unit
- Once the circuit is correct, re-run this guide for the plumbing swap
- Old and new unit data plates (voltage, amperage)
- Photo of the breaker feeding the unit
DIY swap is reasonable — same spec, same location, electric point-of-use
medium confidenceA like-for-like electric point-of-use swap with no electrical, water-routing, or gas changes is a defensible DIY job. Still pull a permit if your jurisdiction requires it.
- Confirm permit requirements with your building department
- Shut off the breaker at the panel; verify dead at the unit's junction box with a non-contact voltage tester before touching wiring
- Close the cold-water shutoff feeding the unit; open the downstream tap to relieve pressure and let the unit drain
- Disconnect water, then electrical; remove old unit
- Mount new unit per its instructions; reconnect water with new flex connectors and fresh PTFE tape on threaded fittings
- Reconnect electrical, restore water FIRST, purge air through the downstream tap, then re-energize the breaker
- Set output temperature no higher than 120°F
- Watch for leaks and verify operation over the next 24 hours
- Only if stuck — photos of where you paused
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