The situation
Illustrative example. Not a real job or customer.
In this example, a Villa Park household replaced a tank water heater in the garage with a tankless unit. It was connected to the existing small gas line that had fed the tank. Single showers are fine, but when two showers run while the furnace is on, the water turns lukewarm and the unit shows an error code.
- The owners call a licensed plumber and describe when the problem happens.
- The plumber reads the tankless unit's maximum input and every other appliance's rating plate.
- The plumber measures the run from the meter and checks the existing pipe size.
- A gas pressure reading is taken at the unit while it and the furnace run at full fire.
The reading drops well below what the unit needs under load, confirming that the supply line is undersized for the combined demand.
Options the plumber presents
| Option | What it involves | Considerations |
|---|---|---|
| Upsize the water heater branch | Replace the existing small pipe with a larger one along the same route | Depends on whether the trunk is large enough |
| Dedicated line from the meter | Run a new, properly sized line directly to the garage | More pipe, but isolates the heater from other loads |
| Upsize the trunk | Replace the main pipe that feeds several appliances | Fixes sizing for future additions too |
| Check meter capacity | Confirm with SoCalGas the meter can supply the total | Needed if total demand rose significantly |
How the fix unfolds
- Plan
- Owners choose a dedicated line, since a spa heater is planned later.
- Permit
- The plumber confirms permit requirements with the City of Villa Park.
- Install
- A new line sized for the tankless unit plus the future spa load is run from the meter.
- Test
- The new piping is pressure tested and inspected.
- Verify
- The plumber rechecks gas pressure at the unit with everything running at once.
Lessons
- Check gas line capacity before buying a tankless water heater
- A plumber should total every appliance, not just the new one
- Error codes under heavy demand can point to the gas supply
- Plan for future appliances when sizing a new line
Questions to ask in a similar case
- What pressure did you measure at the unit under full load?
- Will the new line leave room for other planned appliances?
- Does the venting also need changes for this unit?
Common questions
Is this a real household?
No. The scenario is invented to illustrate a common sizing problem.
Could the heater itself be faulty?
It could. Measuring gas pressure under load helps separate a supply problem from an appliance fault.
Do all tankless conversions need a new line?
Not all, but many do. A load and length calculation tells you before installation.
General information for Villa Park, not a quote or professional advice. In an emergency, call 911.