Quick Answer:
If flow is reduced and you hear air while testing a newly installed water heater, start by following the installer’s flush procedure to purge the tank and trap any sediment. Then run both hot and cold taps to see whether the slow flow is limited to hot lines. Inspect any fittings the installer disturbed, check the nearest cleanout for debris, and snake the branch that serves the affected fixtures if only hot water is slow. Contact the installer or a plumber if flushing doesn’t fix the problem or if you find leaks.
Why This Happens
Installing a water heater can dislodge mineral scale, rust, or small bits of pipe debris. That material can travel into branch lines or collect at fittings and valve seats, causing reduced flow or air in the taps. The situation is similar to other plumbing work that briefly disturbs the system, such as Partial clog after filter install or Partial clog after turning water back on, and usually shows up as reduced flow on hot lines first.
Step-by-Step What to Do
1. Follow the installer’s flush procedure
- Use the exact steps the installer provided to flush the heater. That usually means attaching a hose to the drain valve, opening the valve, and running water until it clears. This purges trapped air and carries sediment out of the tank.
- Collect the water and sediment as recommended (into a floor drain or container) so debris doesn’t enter your drains or landscape.
- Do not improvise with makeshift tools that could damage the drain valve.
2. Run both hot and cold taps to compare flows
- Open a hot tap and a nearby cold tap at the same time. If only the hot tap is weak, the problem is likely in the hot branch or heater outlet. If both are weak, the issue may be upstream in the main supply.
- Check multiple fixtures (kitchen, bathroom, laundry) to map which branches are affected.
3. Inspect and tighten any newly disturbed fittings
- Look at fittings, unions, and valves the installer worked on for loose connections or visible leaks.
- Gently tighten accessible fittings with the proper wrench size—do not overtighten. If a connection leaks after tightening, stop and call the installer or a plumber.
4. Open the nearest cleanout and check for dislodged debris
- Debris can become trapped in branch lines. Open the nearest cleanout to the affected branch to see if sediment or particles were pushed into the line during the install.
- If you see debris, use a manual drain snake or auger sized for that branch to clear it. Focus on the hot-water branch if only hot fixtures are slow.
- Work carefully to avoid damaging piping or seals. If the cleanout is hard to reach or you’re unsure how to proceed, contact a plumber.
5. Call the installer or a plumber if flushing doesn’t restore flow or leaks appear
- If you’ve followed the flush procedure, compared hot and cold flows, inspected fittings, and cleared the cleanout but the problem persists, stop and call the installer or a licensed plumber.
- Also call for help immediately if you discover a leak you cannot stop, or if the heater shows signs of malfunction after flushing.
What Not to Do
- Avoid flushing the heater with improper tools that can break the drain valve or strip threads.
- Do not pour chemicals into the plumbing or the heater to “clear” installation debris—chemical drain cleaners can damage tanks, valves, fixtures, and seals.
- If flushing doesn’t restore flow, you detect leaks, or only hot fixtures remain affected after proper flushing, call the installer or a pro instead of trying invasive repairs beyond your experience.
When to Call a Professional
- Flushing and basic checks don’t restore normal flow.
- Visible or persistent leaks appear at the heater or nearby fittings.
- Only hot fixtures are slow after proper flushing and cleaning of the branch.
- You cannot access the correct cleanout or lack the tools/experience to snake a branch safely.
Safety Notes
- Before doing any work at the heater, follow the installer’s safety instructions. For electric heaters, turn off the breaker; for gas models, follow the manufacturer’s instructions or call the installer if you’re unsure.
- Allow hot water to cool before working on taps or the drain valve to avoid scalding.
- Wear eye protection and gloves when snaking lines or handling drained water and sediment.
- Avoid chemical cleaners that can react with tank materials or create hazardous fumes.
Common Homeowner Questions
- Why do I hear air after the install? Air trapped in the tank or lines during installation is common; flushing the heater and running taps usually clears it.
- How long should flushing take to fix reduced flow? In many cases a proper flush and brief run of hot water will restore flow within minutes; if not, further clearing or professional help is needed.
- Will this void warranty if I do basic flushing myself? Basic flushing and flow checks performed per the installer’s instructions typically do not void warranties, but avoid altering or replacing parts without consulting the installer or manufacturer.
More in this topic
For more related fixes and similar symptoms, see Main Line Partial Clogs.