By Pridemark Plumbing · Licensed Arizona Contractor, ROC #319398
Tankless water heater maintenance in Buckeye, AZ is easy to put off. The heater hangs on the garage wall, the hot water keeps coming, and nothing tells you it’s due until the little display on the heater flashes a code. On a Rinnai, the code to know is LC, which means scale is building up inside.
In September 2026, a homeowner in the Verrado community of Buckeye, Arizona 85396 had Pridemark Plumbing out for the yearly service on their Rinnai tankless. It was planned maintenance, not a repair call. While we were there, we changed the filters on their reverse osmosis (RO) drinking water system and checked the water softener right beside the heater.
The short version: In September 2026, Pridemark Plumbing serviced a condensing Rinnai tankless water heater in Buckeye, Arizona, and read its incoming gas pressure at 7.85 inches of water column (about 0.28 psi), inside the 4.0-to-10.5-inch supply range Rinnai lists for its KCM-series heaters. We flushed the heat exchanger with vinegar, changed three RO filters, checked the RO tank’s air charge and pulled the softener’s injector. Our advice: the yearly licensed inspection Rinnai requires, and a softener that keeps drawing brine.
What Does Tankless Water Heater Maintenance in Buckeye Include?
A yearly inspection by a licensed plumber, built around a heat exchanger flush. The heater on this job has KCM stamped inside, and Rinnai’s KCM-series manual says the appliance “must be inspected annually by a licensed professional.” Here’s what that visit covers on a Rinnai like yours:
- Flushing the heat exchanger, the tubes the burner heats, to clear out scale. Rinnai’s procedure pumps 4 gallons of undiluted white vinegar through it, at 4 gallons a minute, for at least an hour.
- Cleaning the inlet water filter, a small screen where cold water enters.
- Checking the burner for a clear, blue, stable flame, and vacuuming dust off the burner and fan blades.
- Looking over the vent pipes and the condensate line. A condensing heater pulls extra heat out of its own exhaust, and the water that condenses drains through that line.
- Working the pressure relief valve, the hot-side safety valve, by hand once a year.
- Checking the gas, both the pressure reaching the heater and the connections for leaks.
Most of that sits inside the cabinet, so the visit starts with the front cover coming off.
When was your tankless last opened up?
If you can’t remember, it’s probably due. Pridemark Plumbing is based in Surprise and works across the West Valley.
What Did We Find When We Opened This Rinnai?
This one’s a condensing Rinnai, the kind with white plastic vent pipes on top. With the front cover off, you can see the heat exchanger, the burner and controls, and the isolation valves underneath: shutoff valves with built-in service ports that the flush runs through.
Donnie, our plumber on this job, also read the incoming gas pressure with a digital manometer, a gauge built for the very low pressures in a gas line. It read 7.85 inches of water column.
Is 7.85 inches of water column normal gas pressure?
Yes. A reading of 7.85 inches of water column, about 0.28 psi, means a normal home gas supply. Southwest Gas’s Arizona tariff sets standard delivery at a home’s meter at about 0.25 psi, which it also writes as 7-inch water column, so a reading just under 8 inches at the heater is close to that standard.
Rinnai lists a natural gas supply range of 4.0 to 10.5 inches for its KCM-series condensing heaters, and our 7.85 reading sits well inside it.
House gas runs at such low pressure that plumbers measure it in inches of water column, meaning how far up a tube the gas could push water. One psi equals about 27.7 inches. If the flowing supply drops below 4 inches, Rinnai’s KCM tech sheet says the gas supply is inadequate and the unit won’t operate to specification.
Was 7.85 the supply pressure or the burner pressure?
The supply pressure. We read the incoming gas, the gas arriving from your meter. Manifold pressure is the much lower pressure the heater’s own gas valve feeds the burner, and the table in Rinnai’s KCM tech sheet sets it between 1.00 and 3.46 inches of water column on natural gas, depending on the model and the flame. No burner setting comes near 7.85, so the number itself backs that up.
How does a plumber check gas pressure on a tankless water heater?
With a manometer on the heater’s inlet gas test point, while every gas appliance in the house fires at once. That’s Rinnai’s full supply test, and it shows whether your gas line is big enough to keep up. On another job nearby, we found a Navien tankless running on a gas connector rated for less than half of what it needed.
How Often Should You Flush a Tankless Water Heater in Arizona?
As often as your water needs it, since Rinnai doesn’t set a number of months. Its manual says flushing the heat exchanger regularly is required, and more often where water is hard. The heater tells you when. An LC code on the display means scale is building, and Rinnai’s tech sheet warns that repeated LC codes will eventually lock the water heater out.
Rinnai lists a maximum total hardness of 200 milligrams per liter, about 11.7 grains per gallon, and says water in a hard-water area must be treated.
Verrado’s water comes from EPCOR, and it can run harder than Rinnai allows. EPCOR’s 2025 water quality figures for its Agua Fria district show 2 to 17 grains per gallon. At 17 grains, the top of EPCOR’s range, untreated tap water is already past Rinnai’s 11.7-grain limit.
Rinnai also says scale builds faster when the heater’s set at a high temperature, so don’t run yours hotter than you need. And its manual is blunt about the stakes: “Damage caused by lime build-up is not covered by the unit’s warranty.” When scale wins, the fix can be a new heat exchanger. For what that repair takes, see the Rinnai heat exchanger and fan unit we replaced in Buckeye.
Why Check the Water Softener During Tankless Water Heater Maintenance?
Because a softener that’s quietly stopped working sends hard water straight into your tankless, and it’s easy to miss. Rinnai’s own installer checklist includes this line: “Inform the consumer if the isolation valves are not installed or if a water softening system is not installed.” This home has a 32,000-grain softener right beside the Rinnai.
A softener recharges its resin beads, the tiny beads that catch hardness minerals, by pulling salty brine from the brine tank. The injector does the pulling. It’s a small nozzle in the control valve that uses fast-moving water to create suction, like a venturi. Clack’s service manual for its WS1 softener control valve lists a plugged injector as the first cause of a softener that won’t draw brine. Without brine, a softener can deliver hard water.
A plugged injector is hard to spot, because the display lights up and the salt sits there. If your salt level never seems to drop, start there. Our guide to a water softener not using salt walks through it.
What Does an RO Drinking Water System Need Each Year?
Fresh prefilters and the right air charge in its tank. Both affect what comes out of your RO faucet.
The carbon filter matters most on city water. Dow FilmTec rates its home RO membrane, the fine sheet that does the purifying, for less than 0.1 parts per million (ppm) of free chlorine. EPCOR adds chlorine as a disinfectant, and its 2025 Agua Fria figures show 0.77 to 0.95 ppm, so fresh carbon has to catch it before it reaches your membrane.
The air charge is the air pressure in the RO tank, and it’s what pushes water out when you open the RO faucet. With too little air, the faucet runs weak even when the tank’s full. Makers set it with the tank empty, at 5 to 7 psi for APEC and 7 to 10 psi for iSpring. We handle both as part of our water treatment and purification work.
What Did We Do on This Visit?
Six steps, all on one visit, so you know what to expect from yours:
- Opened the Rinnai by taking the front cover off.
- Flushed the heat exchanger with vinegar through the isolation valves’ service ports, then capped them.
- Read the incoming gas pressure with a digital manometer: 7.85 inches of water column.
- Changed three RO filters: the sediment filter, the carbon filter and the final polishing filter.
- Checked the RO storage tank’s air charge.
- Pulled the softener’s injector and checked it for debris.
What Did This Homeowner Get From One Visit?
One appointment for three water systems, and a gas reading on record. If the hot water ever falls short next year, there’s this year’s 7.85 to compare against, so it’s quicker to tell a gas problem from a heater problem. When a West Valley tankless can’t hold its temperature, we check the gas supply before we touch anything inside the heater. Most of the tankless heaters we open on maintenance visits haven’t been opened since the day they went in.
That’s the point of doing it all on one visit, and it’s how we approach plumbing services in Buckeye. One set of eyes sees how your softener, heater and RO affect each other. If you’d rather not keep track, our Service Agreement includes one routine maintenance visit a year, and flushing minerals and sediment from your water heater is part of it.
Want the same tankless service and gas reading at your place? We’ll flush your tankless and read its gas pressure, so you have a number on record for next year. New to Pridemark Plumbing? Show the $30 new-customer coupon on your phone.
Can You Do Tankless Water Heater Maintenance Yourself?
Some of it. Changing RO filters and keeping salt in the softener are homeowner jobs, and plenty of handy homeowners do both. The tankless is different. Rinnai’s manual says repairs and maintenance shall be performed by a licensed professional, and reading gas pressure means opening the gas side of the heater. If your heater shows a code, runs hot and cold, or hasn’t been opened in a year, call a plumber. More on our tankless water heater service.
Questions Homeowners Ask About Tankless Water Heater Maintenance
How often does a tankless water heater need maintenance in Buckeye, AZ?
Once a year. Rinnai requires a yearly inspection by a licensed professional, and the local water makes the flush matter. EPCOR’s 2025 figures for its Agua Fria district, which serves Verrado, show 2 to 17 grains per gallon. Flush sooner if your heater shows an LC code, Rinnai’s sign that scale is building.
What gas pressure does a natural gas tankless water heater need?
Rinnai’s KCM-series condensing heaters list a natural gas supply range of 4.0 to 10.5 inches of water column, read at the inlet test point with every gas appliance running at full fire. Other models differ, so check your heater’s rating plate. In September 2026, Pridemark Plumbing read the incoming gas at 7.85 inches, about 0.28 psi, on a Rinnai in Buckeye, Arizona.
Can low gas pressure make a tankless water heater show an error code?
Yes. Rinnai’s tech sheet puts gas pressure among the first checks for its code 11, when the burner won’t light, and code 12, when the flame goes out. If the supply is lower than the rating plate allows, Rinnai says the heater won’t run to specification. A plumber with a manometer can tell you whether it’s the gas or the heater.
Does a tankless water heater still need maintenance if you have a water softener?
Yes. Rinnai says regular flushing is required, and its yearly inspection covers more than scale: the inlet water filter, the burner flame, the fan, the vent and condensate line, the relief valve and the gas. A working softener slows scale, but if its injector plugs, hard water can reach the heater before anyone notices.
What does an LC code mean on a Rinnai tankless?
An LC code means scale is building inside the heat exchanger and the heater needs a flush. Rinnai’s tech sheet says repeated LC codes will eventually lock the water heater out, so don’t keep clearing it and moving on. A flush clears the scale, and a softener that’s working keeps it from coming back as fast.
Showers running hot and cold? An LC code on the display? Softener salt that never goes down?
Any of those is worth a call. We’re a licensed, local West Valley plumber (ROC #319398). We’ll read your gas pressure, open up and flush your tankless, and pull your softener’s injector, then tell you plainly what we find. If the injector’s plugged, we can clean or replace it.
Call 623.239.2606 Request a visit online
First visit with us? Show the $30 new-customer coupon on your phone.