Weil-McLain AquaBalance Error Codes: A01, F37 and A16

Write down the letter and the number

Weil-McLain says the display flashes with the fault symbol when there is a fault. Write down whether it is A or F and the number, and read the pressure/temperature gauge at the same time.

If the display shows FH after the boiler is powered up, that is not a fault. Weil-McLain’s manual says FH shows for the first 300 seconds and identifies the air purge function.

With an A code, press RESET once

Press the RESET button for 1 second. If the boiler starts and stays running, note the code. If the same A code comes back, Weil-McLain’s corrections are technician work: for A01 they include the gas supply, the ignition and detection electrode, the gas valve, the gas supply pressure and a blocked condensate trap.

Remember the limit of 5 resets in 24 hours. The manual’s warning is not to leave the boiler operating without a complete diagnosis.

With F37 or F20, read the pressure gauge

Weil-McLain calls F37 incorrect system water pressure, too low below 8 psi, and says its boiler water pressure switch is set for 9 psi (plus or minus 2) minimum. Its other F37 corrections, a damaged or disconnected pressure switch and the pump direction on a heating only boiler, are technician work. F20 is a warning that the pressure is near the low level, and the boiler keeps heating.

Read the gauge and look around the boiler, the piping and the relief valve for water. The user’s manual says leaks in the boiler or piping must be repaired at once, by a qualified service technician, and never to add cold water to a hot boiler, because thermal shock can crack the heat exchanger. On the high side, the user’s manual says the gauge should not read above 24 psig, which may point to the expansion tank.

With A06, check the vent and air terminals outside

For A06, Weil-McLain’s corrections include removing any obstruction from the flue, exhaust ducts, air inlet and terminals. A04 is F07, exhaust gas temperature too high, repeated 3 times in 24 hours; Weil-McLain’s F07 corrections, air in the heat exchanger, combustion and water flow, are technician work.

The user’s manual says the boiler shuts itself down if its air or vent is blocked. If the blockage is easily accessible and removable, remove it, and the boiler should attempt to restart within an hour. If the blockage is not obvious or cannot be removed, have the boiler and system checked by a qualified service technician.

With A01, A06 or F15, look at the condensate trap

A blocked condensate trap is in Weil-McLain’s corrections for A01, A06 and F15. Its user’s manual makes the monthly owner check: inspect the condensate drain tubing and its end so condensate can run freely, and inspect the trap under the boiler for sediment, cleaning it out if necessary. Before any maintenance, Weil-McLain says to disconnect the electrical supply and let the boiler cool, to avoid shock and severe burns.

Make sure the trap has water in it. Weil-McLain says to contact a boiler service technician immediately if you find the trap dry, and to contact one if you see any other problem.

With A16 or F39, it is the outdoor sensor

On a heating only boiler, Weil-McLain’s quick start guide says A16 flashes when the unit is powered up with no outdoor sensor connected, and it should not appear on combi boilers. Its fix is to install the outdoor sensor and push reset. A faulty outdoor sensor gives F39, and the boiler manual lists a damaged sensor, shorted wiring, or a sensor disconnected after sliding temperature was turned on. Those are installer jobs.