10 Deadly DIY Tankless Water Heater Installation Mistakes to Avoid

The appeal of DIY is strong. It promises savings and the satisfaction of a job well done. But when it comes to installing a gas appliance like a tankless water heater, the line between satisfaction and catastrophe is razor-thin. As a home safety inspector, I’ve seen the consequences of projects gone wrong. This isn’t a tutorial; it’s a warning. These are the top mistakes that can lead to property damage, serious injury, or worse.

If you have any doubt about your ability to avoid every single one of these, hire a licensed professional.

1. Improper Gas Line Sizing & Connection:

   • The Danger: A gas line that’s too small will starve the appliance, leading to poor performance and soot buildup. Worse, an improperly sealed connection (using the wrong type of tape or dope, or cross-threading) will cause a slow, silent gas leak, turning your home into a time bomb.
   • The Fix: Gas plumbing is not a place to learn. The pipe must be sized for the heater’s massive BTU load and the distance from the meter/tank. Every connection must be tested with a leak detection solution.

2. Catastrophic Venting Errors (Indoor Units):

   • The Danger: This is the #1 killer. Gas appliances produce carbon monoxide (CO), a colorless, odorless poison. Venting an indoor unit with the wrong material (like standard plumbing PVC instead of rated stainless steel or solid-core PVC), an insufficient slope, or too many bends will trap exhaust gases, leaking CO into your home.
   • The Fix: This is a key reason why outdoor units like the Camplux WA528 are an inherently safer choice for DIYers—they completely eliminate the risk of indoor CO buildup. For indoor units, you must follow the manufacturer’s venting specifications to the letter. No exceptions.

3. Ignoring Water Pressure & Quality:

   • The Danger: Extremely high water pressure can damage the unit’s internal components. Hard water, full of minerals, will build up scale inside the heat exchanger, strangling its efficiency and eventually killing it.
   • The Fix: Test your home’s water pressure. If it’s over 80 PSI, install a pressure reducing valve. If you have hard water, install a water softener or commit to a regular descaling maintenance schedule.

4. Using the Wrong Type of Valves:

   • The Danger: A tankless heater requires a specific service valve kit. These valves not only shut off the water but also include a pressure relief valve (a critical safety feature) and ports that allow you to isolate and descale the unit. Using simple ball valves saves a few dollars but makes maintenance nearly impossible and can be unsafe.

5. Incorrect Electrical Grounding:

   • The Danger: The sophisticated electronics in a modern tankless heater are sensitive. An improper ground can lead to circuit board failure or, in a worst-case scenario, create a shock hazard.
   • The Fix: The unit must be connected to a properly grounded electrical outlet. This isn’t just plugging it in; it’s ensuring the entire circuit is safe.

6. Mixing Metals (Galvanic Corrosion):

   • The Danger: Connecting copper pipes directly to galvanized steel pipes creates a chemical reaction that corrodes the fittings, leading to leaks over time.
   • The Fix: Use dielectric unions or brass fittings as a buffer between dissimilar metals.

7. Forgetting Condensate Drainage (Condensing Units):

   • The Danger: High-efficiency condensing units produce acidic condensation. This must be drained away through a dedicated line. If this line gets blocked or isn’t installed, the condensate can back up into the unit, destroying it.

8. Poor Location Choice:

   • The Danger: Installing an indoor unit in a cramped closet without adequate combustion air will starve it of the oxygen it needs to burn cleanly, creating more CO. Installing an outdoor unit where it will be constantly blasted by sprinklers or buried in snow is asking for trouble.

9. Not Following Torque Specifications:

   • The Danger: Overtightening a gas or water fitting can crack it or damage the threads, creating a leak. Undertightening it will also cause a leak.
   • The Fix: Use a wrench, not a gorilla grip. Fittings should be snug, then tightened according to the manufacturer’s spec (e.g., another quarter-turn).

10. Skipping the Final Leak Test:

    • The Danger: Assuming everything is fine.
    • The Fix: Once the installation is complete, you must turn everything on and meticulously check every single water and gas connection for leaks. This final, patient check is the most important step of all.

Your family’s safety is worth more than the money saved on a DIY project. Read this list, be honest about your skills, and when in doubt, make the safe call.