Raypak Digital 406A

The Digital 406A is the largest of Raypak's residential Digital gas heaters. Despite the number, it is not a 406,000 BTU heater: 406A is the model size, and Raypak rates the copper version at 399,000 BTU/h input with 82% thermal efficiency. It has electronic ignition, a digital control with pool and spa modes, and it can go indoors or out with the right top and venting.

Copper or cupronickel

The suffix at the end of the model number is the heat exchanger:

• P-406A-EN-C is copper. Retail listings, including the Amazon one, print it P-R406A-EN-C.
• P-406A-EN-X is cupronickel.

They are not the same heater with a different tube. Raypak's parts list gives each its own heat exchanger, tube bundle and burner tray, and warns that copper and cupronickel parts are not interchangeable: a -C heater takes copper parts, a -X heater cupronickel. The natural gas burner tray for the cupronickel heater carries #51 orifices at sea level, where the copper heater's carries #50, and Raypak's manual rates the cupronickel 406A at 360,000 BTU/h rather than 399,000.

Both take the same water chemistry limits, including 4,500 ppm salt, and both have a ProTek Shield on the inlet.

This page covers the residential P-406A, with polymer headers. The B-406A is the bronze-header ASME version built for commercial use, with its own heat exchanger, headers and high limits, a one-year warranty, and parts that are not listed here.

What the installer has to get right

Raypak's warranty only applies when a properly licensed service provider installs the heater, so most of this is the installer's job. It is worth knowing anyway, because several of these mistakes show up later as a fault the owner calls in.

• Flow between 40 and 100 GPM. Above 100 GPM, which Raypak says usually means a pump larger than two horsepower, an external bypass valve is required.
• Plumbing order. Pump, then filter, then heater, then back to the pool. Salt cells and chemical feeders go downstream of the heater, with a check valve between them, and nothing on the return line may block flow while the pump runs.
• Gas. Natural gas at 6 to 10.5 inches of water column, a sediment trap ahead of the heater, and a manual shutoff outside the cabinet. On the 406A, a 3/4-inch gas line is allowed for no more than 5 feet from the gas valve.
• Power. 120 or 240 volts, factory-wired for 240. Never 208 volts.
• Placement. Not within 3 feet of a heat pump or an outdoor condensing unit, not where sprinklers can spray into it, and not under an overhang less than 3 feet above its top. Outdoors it needs 36 inches clear above the stackless top, 12 inches on the water side and 6 inches at the back and the other side. For service without moving it, Raypak recommends 24 inches in front and 18 inches on the water side. In snow country, Raypak recommends putting it indoors.
• Elevation. The rating holds to 2,000 feet. Above that, input drops 4% per 1,000 feet, and the burner orifices are ordered by elevation from the rating plate.

Water chemistry

Raypak's table for pools other than fiberglass:

• pH 7.6 to 7.8. Below 7.2 the manual says the heat exchanger corrodes.
• Total alkalinity 80 to 120 ppm, calcium hardness 200 to 400 ppm.
• Salt 4,500 ppm maximum.
• Free chlorine 2 to 3 ppm, and never above 5.
• Total dissolved solids 3,000 ppm maximum, or up to 6,000 in a saltwater pool.

Fiberglass pools get a lower pH, 7.3 to 7.4, and higher alkalinity, 120 to 150. Heat exchanger damage from chemical imbalance is not covered, and neither is corrosion from a feeder or chlorinator that is out of adjustment. Never put sanitizer in the skimmer.

Running it

Press MODE for POOL or SPA and set the temperature with the arrows. It goes up to 104°F, and a program setting raises that to 107°F. The heater reads water temperature at its inlet, so the display can disagree with a thermometer in the pool.

Three habits save most service calls:

• Run the pump at least five minutes after the heater stops, so residual heat does not trip a high limit. With a time clock, set it to cut the call for heat 15 to 20 minutes before the pump turns off.
• On a two-speed pump, heat on high speed if low speed is not enough flow. Banging, or shutting off on high limit, are Raypak's signs that it is not.
• Do not run it in cold water for long. Prolonged operation with the pool below 50°F can seriously damage the heater and is not covered. From a cold start, run it continuously until the water is warmer. Do not use it to keep water just above freezing either; freeze-ups are not covered.

To winterize, turn off the gas and power, remove the ProTek Shield, and open the drain plug on the return header.

The service menu

Hold MODE and UP for 3 to 5 seconds and the heater keeps running while it shows:

• Flame strength, as a bar graph. Under four bars is a weak pilot signal.
• Supply voltage to the board. 24 to 29 volts is normal.
• Run time and cycle count.
• Fault history, the last ten faults, most recent first.

There is also a control lockout with a three-digit PIN. Switching the power off will not clear it; resetting the board to factory defaults will, and that also sets both setpoints back to 65°F.

What the display is telling you

• Water Sw Open — the pressure switch is not seeing flow. Clean the filter and strainer first.
• Hi Limit 1 or 2 open — check flow, then the Unitherm Governor and bypass.
• Rollout Sw Open — check for a blocked heat exchanger and soot.
• Sensor Failure, Sensor Open, Sensor Short — the temperature sensor or its wiring.
• Ignition Lockout or Ignition Failure — pilot not lighting or not staying lit. Check the gas, the spark and the pilot orifice.
• Clock/Fireman Sw — a time clock or remote has opened the circuit. Not a fault if that is what you set.
• Low Temp Lockout — water below 36°F.

Maintenance

One month after start-up, then twice a year:

1. Look at the top of the heater and the flue for soot, and clean it. Soot is combustible: wet it first, and never use a steel wire brush.
2. Clean dust and lint from the burners and pilot.
3. Operate the controls, the gas valve and the pressure relief valve.
4. Watch the flame. It should be blue and well defined. Yellow means restricted air openings and lifting means high gas pressure. A low flame means low gas pressure: shut the heater off and call the gas supplier or a qualified service agency.

Check for rodent nests after the heater has sat unused, and check the ProTek Shield, which Raypak's warranty treats as a routine service replacement.

Where Raypak's documents disagree

• The cupronickel rating. The manual gives the P-406A-EN-X 360,000 BTU/h. Raypak's website lists both 406A versions at 399,000.
• The water pressure switch. The manual says the switch is factory-set at 2.0 psi, and its revision note says the setting changed from 1.75. The same manual's parts list still describes 006737F as a 1.75 psi switch.
• The setpoint range. The controls section says the default range is 50 to 104°F; the start-up section says 65 to 104°F.
• The roll-out fuse. The safety section calls it single-use, to be replaced once it trips. The diagnostic chart says to press a manual reset button.
• One burner tray. 019229F is printed as a natural gas tray inside the cupronickel propane group. Confirm it with Raypak before ordering.
• The model number. Retail listings add an R, P-R406A-EN-C; the manual prints P-406A-EN-C.

Check the seller before you buy

• Two years of parts and labor at a single-family home, from a licensed install. One year anywhere else, and one year on the bronze-header ASME 406A.
• In the United States, only from an authorized dealer. Raypak reserves the right to reject claims on heaters bought from unauthorized internet sites or marketplace storefronts.

The heater is the same either way; the warranty is not. The Raypak brand page has the rest.