Quick Answer:
If your tankless loses flow or throws error codes after debris appears in your water, the inlet screen and the heat exchanger are likely partially blocked. Start by powering down the unit, clean the inlet screen, perform the manufacturer-recommended flush of the heat exchanger, check the flow sensor, and consider adding a pre-filter or strainer upstream to catch future debris.
Why This Happens
Work on municipal lines, curb stops, or disturbances inside older pipes can loosen sand, grit, and pipe scale. That material travels with the water and collects at the first narrowing inside your heater: the inlet screen, the flow sensor area, and later the heat exchanger passages. Homeowners commonly see reduced flow, error codes, or intermittent heating after such events — a common example is Sediment buildup after curb stop work.
Step-by-Step What to Do
1. Power down and isolate the unit
- Turn off the gas or electrical supply following the unit manual.
- Shut the cold-water inlet valve to stop water entering the heater.
- Open a nearby hot faucet to relieve pressure before opening service ports.
2. Clean the inlet screen
- Locate the inlet screen (consult your manual — usually at the cold-water inlet or inside a service cover).
- Remove the screen or strainer and rinse it under clean running water. Use a soft brush to remove trapped grit; avoid metal tools that could damage the mesh.
- Reinstall the screen and any gaskets per the manual’s torque or seating guidance.
3. Perform the manufacturer-recommended flush
- Attach the service hoses to the unit’s service valves, set the loop with a bucket or pump, and follow the manual for the correct cleaning solution and procedure. Many manufacturers allow a white-vinegar descaling unless they specify a proprietary solution.
- Run the flush for the time the manual recommends, then thoroughly rinse with fresh water to remove acidic residue.
- If you see continued debris after flushing, repeat once more or proceed to inspect the heat exchanger more closely.
4. Check the flow sensor
- Inspect the flow sensor area for lodged particles. Some sensors have removable parts designed to be rinsed; others require a gentle wipe.
- Do not use sharp tools on sensors; if the sensor remains out of spec or damaged, it may need replacement.
- Clearing sensor debris often resolves codes related to low flow or inlet pressure — a typical symptom of Pressure loss due to sediment buildup.
5. Inspect the heat exchanger and final checks
- If performance is still poor after the flush and inlet cleaning, the heat exchanger passages may be heavily fouled. Some units allow partial disassembly for inspection; many do not — consult your manual.
- Close service valves, restore inlet water, and slowly reopen supply. Watch for leaks and reapply power only after you confirm the system is water-filled and stable.
6. Install a pre-filter or strainer upstream
- If your supply carries debris often, install a sediment strainer or a dedicated pre-filter before the heater. Choose a model rated for the expected debris size and flow rate and install it on the cold-water inlet side.
- Service the strainer regularly; catching debris before it reaches the unit prevents repeat clogs.
What Not to Do
- Don’t keep resetting tankless errors without cleaning the inlet screen and flushing. Repeated resets can hide a developing problem and cause damage.
- Don’t use metal wire brushes or sharp implements inside screens, flow sensors, or the heat exchanger — they can cause permanent damage.
- Don’t run the unit with service valves closed or operate the heater dry. Always confirm water flow before restoring power or gas.
- Don’t mix cleaning chemicals — follow the manufacturer’s approved cleaning agent and concentrations.
When to Call a Professional
- If the unit still shows error codes or low-flow symptoms after you clean the inlet screen and perform the recommended flush.
- When the heat exchanger appears heavily clogged or corroded — deep internal cleaning or part replacement can require tools and parts not suited for DIY.
- If you’re uncomfortable isolating gas or electrical supplies, or if leaks appear after reassembly.
Safety Notes
- Always follow the unit manufacturer’s safety instructions. Turn off gas and/or electricity before working on the unit.
- Relieve system pressure before opening service ports. Hot water and steam can cause burns.
- Use only recommended cleaning agents and protective gloves and eye protection when flushing or handling debris.
Common Homeowner Questions
- How often should I flush? Flush at least once a year, more often if your water is hard or carries debris.
- Can I use plain white vinegar to flush? Many manufacturers allow white vinegar, but always check the manual first — some require a specific solution.
- Will a screen fix all sediment problems? A screen helps but won’t stop very fine particles or scale; a proper pre-filter and regular flushing are the best prevention.