Flush and descale: why scale builds up and how the flush works
Heating water makes dissolved minerals drop out as scale, and a tankless heat exchanger has narrow passages that scale clogs. The Grand Rapids water system, which supplies Allendale Township, reports a 2025 plant-tap average of 8.3 grains per gallon (142 mg/L). That is a system average, not a reading at your tap, so test your tap before you decide how often to flush.
Scale shows up as swinging temperatures, weaker flow, kettle-like noises or a scale or overheat code. A vinegar flush circulates a mild acid through the exchanger to dissolve it, then rinses clean. The steps look like this at a high level.
Shut it down
Turn off the power and gas, and close the isolation valves on the water lines.
Connect and circulate
Hoses go on the service ports, and a small pump moves white vinegar through the exchanger.
Drain and rinse
The vinegar is drained, the unit is rinsed with clean water and the inlet filter is cleaned.
Restore and test
Valves reopen, the air is purged, the unit is powered up and checked for leaks and a steady temperature.
When to call instead of flushing it yourself
Call us if your unit has no isolation valves or service ports, since adding them is a plumbing job. Call if you are unsure about a gas unit, if a scale code returns soon after a flush, or if anything leaks, which is a water heater repair job. A flush done without closing the gas is a safety risk.
Landlords with units in rentals near the GVSU campus should schedule flushes on a calendar rather than waiting for a complaint. Tenants rarely know that a tankless heater needs descaling, and a unit that is ignored will often announce itself with a cold shower.
Tankless vs tank: how they compare in a real house
| Tank | Tankless | |
|---|---|---|
| Hot water | A stored amount, then recovery | Continuous, up to the flow rate limit |
| Space | Floor footprint | Compact wall unit |
| Gas line | Existing line usually fine | May need a bigger line |
| Venting | Standard flue | Dedicated vent, often plastic |
| Electric units | Standard circuit | Heavy circuit, sometimes a panel upgrade |
| Upkeep | Flush and anode rod | Scheduled descaling |
| Repair | Lower parts cost, easier access | Specialized parts, but a failed unit is rarely wasted |
A tank usually wins on upfront cost. A tankless unit wins on space and on endless supply.
Gas line and venting: the part that surprises people
A tankless gas unit fires hard when it runs, so a gas line sized for a tank burner can be too small. Venting is different too. Many units need a dedicated exhaust, often plastic, plus a condensate drain, with clearances to windows and the ground. An electric unit may need a heavy circuit and a look at the panel.
In many houses, the support work costs more than the heater. If a tank is working and the supporting work will be large, we will tell you that staying with a tank is the better buy. For a broader look at the planned route, see water heater installation.
Error codes and what they usually point to
Codes differ by maker, so check the manual. These are the common families, not a brand guide.
Ignition or no flame
Gas supply, igniter, flame sensor or a blocked vent can stop the burner from lighting.
Overheat or high limit
Scale, low flow or a sensor fault can push the exchanger past its limit.
Vent or exhaust fault
A blocked, disconnected or iced-over vent trips the safety circuit.
Low flow or flow sensor
A clogged inlet filter, partly closed valve or failed sensor can keep the unit from starting.
Scale or maintenance
The unit is telling you the exchanger needs a flush.
Allendale: GVSU-area rentals and newer builds
About 47% of households in the Allendale CDP rent, and GVSU reports 21,382 students across all campuses in Fall 2026. Shared houses where several people shower back to back are where on-demand heating earns its keep. Those same houses are where nobody schedules a flush, whether in Allendale or nearby Hudsonville.
About 32% of township homes were built since 2010. If you bought a newer house, check whether the water heater is a tankless unit, because its first service is easy to miss.
Source: ACS 2020-2024 estimates, GVSU enrollment snapshot, Grand Rapids Water System 2025 average water analysis.
Tankless unit acting up?
Call the line, tell us the code or the symptom and we will tell you whether it needs a flush, a part or a visit.
Call (855) 575-2890What affects tankless install, repair and flush cost
A clear price comes first, and dollar figures stay off the page because tankless jobs vary widely.
A flush is far smaller than a new installation with gas line and vent work.
Line size, vent material and run length are the biggest swing factors.
A heavy circuit, a panel check or new wire adds cost on electric units.
Adding service valves makes every future flush easier and adds to a first visit.
Heavy scale may need a longer flush or point to a part replacement.