How to Flush a Parks Tankless Water Heater

Why and when to flush your Parks tankless water heater

Flushing a Parks tankless water heater removes mineral buildup inside the heat exchanger—the part that warms your water. Hard water deposits (mostly calcium and magnesium) accumulate over time and reduce heating efficiency, raise energy costs, and can eventually damage the unit. Parks recommends flushing annually in areas with moderate to hard water, or every six months if your water is very hard.

You'll know it's time when your water takes longer to heat, the unit cycles on and off more often, or your hot water output drops. Flushing is preventive maintenance, not a repair—doing it regularly keeps the unit running at full capacity and extends its lifespan by years.

Key Takeaways

• Parks tankless water heaters need flushing annually (or twice yearly in hard water areas) to remove mineral deposits that reduce efficiency.
• The flush uses a submersible pump, a five-gallon bucket, and food-grade white vinegar or a commercial descaling solution designed for tankless units.
• The process takes 30 to 45 minutes and involves connecting hoses to the service ports, running vinegar through the heat exchanger, and flushing with clean water.
• You can do this yourself if you're comfortable with basic plumbing connections, or hire a licensed technician to handle it.
• Skipping flushes voids the warranty on many Parks models and can lead to costly repairs within a few years.

What you need to flush a Parks tankless water heater

Gather these items before you start: a submersible pump (a small electric pump that sits in a bucket), a five-gallon bucket, two lengths of hose that fit your Parks unit's service ports, food-grade white vinegar (or a commercial descaling solution made for tankless heaters), a wrench or socket set, towels, and a bucket for draining water that comes out during disconnection.

The service ports are usually labeled on the unit itself—one inlet (cold water side) and one outlet (hot water side). Check your Parks manual to confirm their location and the hose size they accept. Most residential Parks models use half-inch ports. If you don't have the manual, Parks publishes them online by model number, or you can call a local technician to confirm the port size before you buy hoses.

Do not use regular household vinegar with unknown acidity. Food-grade white vinegar (5 percent acidity) or a Parks-approved descaling solution works; some owners use CLR or similar products, but check your manual first—some Parks models specify against certain chemicals. The wrong solution can damage internal seals.

Step-by-step flushing process

Step 1: Turn off the unit and let it cool. Switch off the power at the breaker and close the cold water inlet valve. Wait at least 30 minutes for the heat exchanger to cool. This prevents burns and protects internal components.

Step 2: Drain the unit. Open the hot water tap at a nearby sink to relieve pressure inside the lines. Then open the drain valve (usually at the bottom of the unit) and let water run into a bucket until it stops. Close the drain valve when empty.

Step 3: Connect the pump and hoses. Attach one hose to the cold water service port (inlet) and run it into your five-gallon bucket. Attach the second hose to the hot water service port (outlet) and run it back into the same bucket. Place the submersible pump in the bucket. This creates a closed loop so vinegar circulates through the heat exchanger and back into the bucket.

Step 4: Fill the bucket with vinegar. Pour food-grade white vinegar into the bucket until it reaches the level where both hoses sit submerged. The pump will draw vinegar up through the inlet hose, through the unit, and back out the outlet hose.

Step 5: Run the pump for 30 to 45 minutes. Turn on the submersible pump and let it circulate vinegar through the heat exchanger. You may hear gurgling or see sediment in the bucket—this is normal and means the vinegar is breaking down deposits. Do not leave the pump running unattended; stay nearby to watch for leaks at the hose connections.

Step 6: Drain the vinegar and flush with clean water. Turn off the pump. Disconnect the hoses and let any remaining vinegar drain into the bucket. Refill the bucket with fresh water, reconnect the hoses, and run the pump for another 10 to 15 minutes to rinse the heat exchanger. Repeat the rinse cycle one more time to remove all vinegar residue.

Step 7: Reconnect and restart. Disconnect the hoses and pump. Close the service ports (or reconnect them if they have caps). Open the cold water inlet valve. Turn the power back on at the breaker. Run hot water at a sink for a minute to purge air from the lines, then check for leaks at all connection points.

When to call a professional instead

If you're not comfortable working with plumbing connections, or if your Parks unit is still under warranty, hire a licensed plumber or HVAC technician to handle the flush. Many warranty agreements require professional maintenance to stay valid, so check your paperwork before you start.

Also call a professional if you notice leaks during the process, if the unit won't restart after flushing, or if water pressure drops significantly after you reconnect everything. These signs suggest a problem beyond simple mineral buildup—possibly a failed internal valve or a cracked fitting that flushing exposed.

How often to flush and what happens if you don't

Parks recommends annual flushing for most climates. If your area has very hard water (over 10 grains per gallon), flush twice yearly. You can request a water hardness test from your local water utility—many provide them free or for a small fee.

Skipping flushes causes mineral scale to thicken inside the heat exchanger. Over time, the unit works harder to push water through the clogged passages, raising your energy bill and reducing hot water output. Eventually, the scale can crack the heat exchanger or block water flow entirely, forcing a replacement that costs $800 to $1,500 or more. Many Parks warranties explicitly require regular flushing; skipping it voids coverage.

Frequently Asked Questions

Can I use regular household vinegar instead of food-grade?

Regular household vinegar often has unknown acidity levels and may contain additives. Food-grade white vinegar (5 percent acidity) is consistent and safe for tankless units. Some owners use commercial descaling solutions made for tankless heaters, which work faster but cost more. Check your Parks manual to confirm what's approved for your model.

What if I don't have a submersible pump?

You can rent one from most hardware stores for $10 to $20 per day. Some plumbers sell or loan them. Without a pump, you cannot create the closed-loop circulation needed to flush the heat exchanger effectively, so this step is not optional.

How do I know if my water is hard?

Contact your local water utility and ask for a hardness report—many provide them free. You can also buy an inexpensive test kit at a hardware store. Hard water typically has a white or chalky buildup on faucet aerators and shower heads. If you see that, flush your Parks unit twice yearly instead of once.

Will flushing fix low water pressure or temperature?

Flushing may restore pressure and temperature if mineral buildup is the cause. However, if pressure or temperature remains low after flushing, the problem is likely a failed valve, a clogged filter, or a gas supply issue—call a technician to diagnose.

Do I need to turn off the gas or electricity before flushing?

Yes. Turn off power at the breaker and close the cold water inlet valve before you start. This prevents the unit from trying to heat while you're working on it and protects you from burns or electrical hazard.