A tankless water heater in Dedham, MA heats water only when a tap opens, using a gas burner or electric elements around a compact heat exchanger. There is no storage tank to rust through, but there is a narrow heat exchanger, and mineral scale is its main enemy.
A licensed plumber can install a unit, diagnose error codes, repair parts and descale the exchanger. This page starts with the water, because the water decides how you maintain the unit.
What Dedham water does inside a tankless heat exchanger.
The Dedham-Westwood Water District reported average hardness of 6.0 grains per gallon in its 2025 water quality report, with samples ranging from 4.3 to 7.8 (74.1 to 134 ppm as calcium carbonate, sampled May 30, 2025). That is moderately hard water, mostly calcium and magnesium. The District also adjusts pH and adds orthophosphate for corrosion control, which protects pipes but does not remove hardness.
For a tankless unit, hardness matters because heat drives minerals out of the water as scale on the hottest surfaces. Scale narrows the flow channels, so the unit works harder, throws error codes or delivers weaker output. Treat flushing as routine upkeep in this water, not as an optional extra.
Tankless flush and descale, step by step.
Flushing circulates a descaling solution through the heat exchanger to dissolve mineral buildup, then rinses it clear. Follow the manufacturer's manual for the interval and solution, and know that harder water usually calls for more frequent service. A plumber will typically do the following:
- Shut off the gas or power and the water supply to the unit..
- Close the isolation valves and open the service valves on the hot and cold lines..
- Connect hoses and a small pump to circulate the descaling solution through the exchanger..
- Circulate for the time the manual specifies, then drain the solution..
- Rinse with clean water, clean the inlet filter screen and close the service ports..
- Restore power or gas, restart the unit and check the output and error history..
If your unit has no service valves, ask the plumber to add them. Without them, a proper flush is hard to do.
Ready to book a tankless flush, repair or install? Call to set a time.
Call (617) 752-0573Signs your tankless heater needs attention.
- An error code on the display that returns after a reset.
- Hot water that cuts out or surges mid-shower, the so-called cold-water sandwich.
- Lower flow than the unit gave when new.
- Rumbling or whistling from the heat exchanger.
- A fan or igniter that clicks without lighting on a gas unit.
- A long delay before hot water arrives at a distant fixture.
When service becomes a repair.
A flush clears scale, but it cannot fix a failed part. Plumbers also replace igniters, flame sensors, flow sensors, fans, thermistors and control boards, and clear blocked inlet screens. If the exchanger itself is leaking or badly corroded, replacing the unit may cost less than the part.
If your tankless unit has stopped heating entirely, water heater repair covers the emergency steps, and a failed unit may lead to water heater replacement.
Is tankless right for your Dedham house? A decision table.
| Question | If yes | If no. |
|---|---|---|
| Is there a gas line near the heater, or capacity in the panel? | Install is straightforward | Budget for new line or circuit. |
| Can the unit vent outdoors through a short, clear path? | Fewer venting costs | Longer vent runs add labor. |
| Do two showers run at once? | Check unit capacity carefully | A smaller unit may do. |
| Are you willing to service it on a schedule? | Fits well | A tank may suit you better. |
The Dedham Master Plan reports that about 74% of the town's houses were built before 1978, so many homes have old basements and vent paths. Ask the plumber to inspect the route before quoting a tankless install, since venting and gas sizing often drive the cost.
Gas line, venting and electrical needs.
A gas tankless heater can draw more gas at once than a typical tank burner, so ask whether the gas line needs upgrading. It also needs sealed venting and combustion air. An electric unit needs a heavy dedicated circuit and a panel with spare capacity. Any plumbing change like this needs a permit.
Mass.gov says permits are issued only to licensed plumbers, and in Dedham they go through the Building Department's Plumbing/Gas Division. If you smell gas at any time, leave the building, call 911 from outside, and call your gas utility.
Tankless service and install quotes.
- The unit itself, by fuel, capacity and model.
- Gas line resizing, vent kit, condensate drain or electrical circuit.
- Isolation and service valves, if missing.
- Descaling solution, labor and any filter or softener recommendation.
- Permit and disposal of the old tank, if you are converting.
Homeowner policies generally cover sudden and accidental damage rather than wear and tear, so scale damage is typically not a claim. Want your real number? Call (617) 752-0573.
Before the plumber arrives.
- Write down the model, the error code and what you saw or heard.
- Clear space around the unit and the isolation valves.
- Note any change in water pressure at other fixtures.
- Tell the plumber if the house has a water softener or filter, since that changes the scale picture.
- Plan for the hot water to be off for part of the visit.
Planning a new install or a fuel change? See water heater installation. We also dispatch to Needham.
Frequently asked questions.
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Follow the manufacturer's manual for the interval, then shorten it if you notice scale symptoms. Dedham's average of 6.0 grains per gallon is moderately hard, so a plumber may suggest checking the unit more often than the minimum.
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If scale is the cause, often yes. If the code points to a sensor, igniter or fan, the part needs replacement. A plumber can read the code history before deciding.
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Not necessarily. A softener or scale filter reduces scale, and some manufacturers have conditions on warranties. Check your manual and ask the plumber for an opinion based on your water.
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Some owners do, using service valves and a pump. Gas and electric work around the unit is a risk, and mistakes can cause leaks or void a warranty. Call a plumber if the unit has no service valves or if you are unsure.
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Common causes include scale, a low-flow situation where the unit shuts off, or a mixing problem. A flush and flow test can sort it out.
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A new install or a fuel change does. A licensed plumber pulls it through the Building Department's Plumbing/Gas Division.
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The landlord is usually responsible for a fixed appliance. About three in ten Dedham households rent, so tell your landlord in writing and ask for a service visit.
Codes, standards and sources.
Plumbing work in Massachusetts is governed by 248 CMR 10.00, the Uniform State Plumbing Code, and plumbers are licensed by the Board of State Examiners of Plumbers and Gas Fitters. You can read the state's consumer fact sheet on plumbers and gas fitters before you hire anyone.
Local facts on this page come from the Dedham-Westwood Water District, the Town of Dedham, the other towns named and Mass.gov, and were checked in October 2026. Where a fact could not be confirmed, the page says to ask the utility or the town.