Weil-McLain boiler error codes, lockouts and how to reset

Weil-McLain Ultra Series 1 and 2 error code E02: ignition failed after 5 tries

Checked October 2026

Short answer On Weil-McLain Ultra Series 1 and 2 boilers, E02 is a hard lockout: ignition failed after five attempts. It needs a manual reset; the checks behind it (spark, gas supply, gas valve, venting) are technician work. See what to check

What it means

E02 is a hard lockout on Weil-McLain Ultra Series 1 and 2 boilers: the control tried to light the burner five times and failed. The quick-reference lists print it “Igntion failed after 5 retries”, with the misspelling as printed (ultra-gas-series-2-control-supplement, p. 21; ultra-series-1-boiler-manual, p. 41). The display flashes the first digit, “E” and the two-digit code, and the boiler stays off until a manual reset (ultra-gas-series-2-control-supplement, pp. 21, 28).

The troubleshooting table splits E02 by what happened during the attempts: no spark, a spark but no flame, or a flame with a weak flame signal. Each case has its own list of checks (ultra-gas-series-2-control-supplement, pp. 28–29).

Check these first

The Ultra Series 2 user’s manual has no code list and gives the owner no steps for E02 (ultra-gas-series-2-users-manual).

1. If you smell gas, stop and follow the steps at the top of this page.
2. The boiler stays off until a manual reset (ultra-gas-series-2-control-supplement, p. 21). The Ultra Series 2 user’s manual says that if the boiler will not operate when there is a call for heat and the piping is not hot, you follow “To turn off gas to the appliance” and call your service technician or gas supplier (ultra-gas-series-2-users-manual, p. 9, step 11). The restart after a hard lockout is described in the control supplement and the Ultra Series 1 Boiler Manual, documents for installers and service technicians: the RESET button on the Ultra display panel (ultra-gas-series-2-control-supplement, pp. 9, 21; ultra-series-1-boiler-manual, p. 32).
3. Call a qualified service technician. The E02 lists cover the ignition electrode and its cable, the gas supply and gas valve, the vent and air piping, the condensate drain, the burner and heat exchanger, grounding and the control module (ultra-gas-series-2-control-supplement, pp. 28–29).

When to call a licensed technician

All three cases are technician work (ultra-gas-series-2-control-supplement, pp. 28–29):

• No spark. The ignition electrode cable, its connectors and the ground lead are inspected, and the igniter wire’s resistance is tested.
• Spark, but no flame. The list starts with the manual gas valve inside the boiler and, on models 80 and 105 only, the plastic line from the gas valve to the air inlet elbow. It goes on to the incoming gas pressure (“If gas pressure is too high, the gas valve regulator will lock up.”), obstructions and air in the gas lines, the vent and air piping (“Restricted vent will not allow boiler to light.”), checks at the gas valve, gas flow at the meter, cleaning the ignition electrode, restrictions in the condensate drain fitting and trap, cleaning the heat exchanger, the venturi gas line and flue gas recirculation. The last step is replacing the gas valve.
• Flame, but a weak flame signal. The flame is inspected at low and high fire, the electrode and burner are cleaned, and the gas flow is measured at the meter at high fire; if the input is not within about 10% of the boiler rating, the gas valve is replaced. The ground path is checked, and the last step is replacing the control module.

Related codes: E03, E00, E07. All Weil-McLain codes

Weil-McLain Ultra Series 1 and 2 error code E03: ignition or gas valve electrical problem

Checked October 2026

Short answer On Weil-McLain Ultra Series 1 and 2 boilers, E03 is a hard lockout. The service guide's table calls it an ignition failure or gas valve electrical problem; its quick-reference list says internal control failure. Gas valve and control checks are technician work. See what to check

What it means

E03 is a hard lockout on Weil-McLain Ultra Series 1 and 2 boilers. The display flashes the first digit, “E” and the two-digit code, and the boiler stays off until a manual reset (ultra-gas-series-2-control-supplement, pp. 21, 28).

What E03 stands for depends on which Weil-McLain list you read. The troubleshooting table says “Ignition failure or gas valve electrical problem” (ultra-gas-series-2-control-supplement, p. 29). The quick-reference lists say internal control failure (ultra-gas-series-2-control-supplement, p. 21; ultra-series-1-boiler-manual, p. 41). The steps in the table follow its own wording and split the code by timing:

• if E03 appears before the boiler tries for ignition, the problem may be the gas valve connection or its harness;
• if it appears after 5 ignition retries, it “indicates same condition as E-02”, the ignition failure lockout (ultra-gas-series-2-control-supplement, p. 29).

Check these first

The Ultra Series 2 user’s manual has no code list and gives the owner no steps for E03 (ultra-gas-series-2-users-manual).

1. If you smell gas, stop and follow the steps at the top of this page.
2. The boiler stays off until a manual reset (ultra-gas-series-2-control-supplement, p. 21). The Ultra Series 2 user’s manual says that if the boiler will not operate when there is a call for heat and the piping is not hot, you follow “To turn off gas to the appliance” and call your service technician or gas supplier (ultra-gas-series-2-users-manual, p. 9, step 11). The restart after a hard lockout is described in the control supplement and the Ultra Series 1 Boiler Manual, documents for installers and service technicians: the RESET button on the Ultra display panel (ultra-gas-series-2-control-supplement, pp. 9, 21; ultra-series-1-boiler-manual, p. 32).
3. Call a qualified service technician. Every step in the E03 row is on the gas valve, its harness, the ignition checks of E02 or the control module (ultra-gas-series-2-control-supplement, p. 29).

When to call a licensed technician

• E03 before ignition. The row has the technician test the gas valve harness for continuity and the gas valve itself for resistance, between its pins and from each pin to ground (ultra-gas-series-2-control-supplement, p. 29).
• E03 after five retries. The technician follows the E02 troubleshooting: ignition electrode and cable, gas supply and gas pressure, vent and air piping, condensate drain, burner and gas valve (ultra-gas-series-2-control-supplement, pp. 28–29).
• The last step of the row is replacing the control module (ultra-gas-series-2-control-supplement, p. 29).

E07, “Gas valve relay error”, is a separate code; its row checks whether the gas valve wiring is shorted to ground and whether the gas valve is defective (ultra-gas-series-2-control-supplement, p. 30).

Related codes: E02, E07. All Weil-McLain codes

Weil-McLain Ultra Series 1 and 2 error code E04: power lost after lockout

Checked October 2026

Short answer On Weil-McLain Ultra Series 1 and 2 boilers, E04 is a hard lockout: voltage was lost after a lockout, or the incoming power fluctuated. The boiler restarts only after a manual reset; the fixes in the service guide are technician work. See what to check

What it means

E04 is a hard lockout on Weil-McLain Ultra Series 1 and 2 boilers. The display flashes the first digit, “E” and the two-digit code, and the boiler stays off until it is reset by hand (ultra-gas-series-2-control-supplement, pp. 21, 28).

The troubleshooting table gives E04 two triggers: power was interrupted while another error was present, or the incoming power fluctuated (ultra-gas-series-2-control-supplement, p. 30). The same row names where the fluctuations come from: a power failure, a brown-out, or poor electrical input from a back-up generator. It also says the control module will only restart with a manual reset, even after power loss, so the boiler does not come back on by itself when the power returns.

Check these first

The Ultra Series 2 user’s manual has no code list, so it gives the owner no steps for E04 (ultra-gas-series-2-users-manual).

1. If you smell gas, stop and follow the steps at the top of this page.
2. Do not expect the boiler to restart when the power comes back. The control module restarts only with a manual reset (ultra-gas-series-2-control-supplement, p. 30).
3. The Ultra Series 2 user’s manual says that if the boiler will not operate when there is a call for heat and the piping is not hot, you follow “To turn off gas to the appliance” and call your service technician or gas supplier (ultra-gas-series-2-users-manual, p. 9, step 11). The restart after a hard lockout is described in the control supplement and the Ultra Series 1 Boiler Manual, documents for installers and service technicians: the RESET button on the Ultra display panel (ultra-gas-series-2-control-supplement, pp. 9, 21; ultra-series-1-boiler-manual, p. 32). The E04 row’s fixes for poor incoming power are technician work (ultra-gas-series-2-control-supplement, p. 30).

When to call a licensed technician

• E04 that comes back. For shutdowns caused by poor power, the table’s fix is a Weil-McLain Time Delay Relay, part number 383-500-021, which delays incoming power by 3 minutes so it can stabilize before it reaches the boiler (ultra-gas-series-2-control-supplement, p. 30). Fitting it is technician work on the boiler’s power supply.
• Severe power fluctuations. The table says the relay may not solve E04 in severe cases, and that an incoming power line filter or an uninterruptible power source (UPS) may correct it (ultra-gas-series-2-control-supplement, p. 30).
• The fault behind the E04. E04 is set when power is interrupted while another error is present (ultra-gas-series-2-control-supplement, p. 30). The supplement’s note on overrun lockouts says a service technician must troubleshoot the cause and correct it before the boiler goes back into operation (ultra-gas-series-2-control-supplement, p. 9).

Related codes: E05, E06, E11. All Weil-McLain codes

Weil-McLain Ultra Series 1 and 2 error code E05: internal control or display error

Checked October 2026

Short answer On Weil-McLain Ultra Series 1 and 2 boilers, E05 is a hard lockout worded 'Internal Control or Display error' in the service guide. The guide's fix is replacing the display and its ribbon cable, then the control module, which is technician work. See what to check

What it means

E05 is a hard lockout on Weil-McLain Ultra Series 1 and 2 boilers that points at the boiler’s electronics: the display or the control module. The troubleshooting table words it “Internal Control or Display error” (ultra-gas-series-2-control-supplement, p. 30). The display flashes the first digit, “E” and the two-digit code, and the boiler stays off until a manual reset (ultra-gas-series-2-control-supplement, pp. 21, 28).

The E05 row has two steps, and neither is a reset: replace the display and the display ribbon cable, then replace the control module (ultra-gas-series-2-control-supplement, p. 30). That sets E05 apart from the internal failure codes E06, E08, E09, E15, E16 and E17, whose rows begin “Reset control and retry. If problem persists, replace control module.” (ultra-gas-series-2-control-supplement, p. 30).

Check these first

The Ultra Series 2 user’s manual has no code list and gives the owner no steps for E05 (ultra-gas-series-2-users-manual).

1. If you smell gas, stop and follow the steps at the top of this page.
2. The boiler stays off until a manual reset (ultra-gas-series-2-control-supplement, p. 21). The Ultra Series 2 user’s manual says that if the boiler will not operate when there is a call for heat and the piping is not hot, you follow “To turn off gas to the appliance” and call your service technician or gas supplier (ultra-gas-series-2-users-manual, p. 9, step 11). The restart after a hard lockout is described in the control supplement and the Ultra Series 1 Boiler Manual, documents for installers and service technicians: the RESET button on the Ultra display panel (ultra-gas-series-2-control-supplement, pp. 9, 21; ultra-series-1-boiler-manual, p. 32).
3. Call a qualified service technician. Both steps in the E05 row are part replacements (ultra-gas-series-2-control-supplement, p. 30).

When to call a licensed technician

• Any E05. Replacing the display and its ribbon cable, and then the control module, is technician work inside the boiler’s control (ultra-gas-series-2-control-supplement, p. 30).
• E05 that returns after the boiler has been restarted. The row has no other step than the two replacements (ultra-gas-series-2-control-supplement, p. 30).

Related codes: E06, E11, E44. All Weil-McLain codes

Weil-McLain Ultra Series 1 and 2 error code E18: outlet water above 210°F

Checked October 2026

Short answer On Weil-McLain Ultra Series 1 and 2 boilers, E18 is a hard lockout: outlet water went above 210°F. At 203°F the control shows soft lockout b18 instead. It needs a manual reset, and Weil-McLain says a service technician must find and correct the cause. See what to check

What it means

E18 is a hard lockout on Weil-McLain Ultra Series 1 and 2 boilers: the outlet (supply) water temperature went above 210°F. The troubleshooting table calls it a “Thermal overrun condition” (ultra-gas-series-2-control-supplement, p. 31).

The supplement describes two levels of overrun protection. At 203°F on the supply or the return, the control shows a soft lockout, b18 for the supply or b19 for the return, and does not fire the burner again until the water has dropped 9°F below the target temperature. At 210°F it goes into hard lockout and shows E18 for the supply or E19 for the return (ultra-gas-series-2-control-supplement, p. 9). A soft lockout restarts by itself once the condition is corrected or times out (ultra-gas-series-2-control-supplement, p. 17); E18 does not.

Check these first

The Ultra Series 2 user’s manual has no code list and gives the owner no steps for E18 (ultra-gas-series-2-users-manual).

1. If you smell gas, stop and follow the steps at the top of this page.
2. The Ultra Series 2 user’s manual says that if the boiler will not operate when there is a call for heat and the piping is not hot, you follow “To turn off gas to the appliance” and call your service technician or gas supplier (ultra-gas-series-2-users-manual, p. 9, step 11). The restart after a hard lockout is described in the control supplement and the Ultra Series 1 Boiler Manual, documents for installers and service technicians: the RESET button on the Ultra display panel. The supplement’s note right after the E18 description adds that a service technician must troubleshoot the cause and correct it before the boiler goes back into operation (ultra-gas-series-2-control-supplement, p. 9; ultra-series-1-boiler-manual, p. 32).
3. Call a qualified service technician.

When to call a licensed technician

• Checking the temperature reading. The E18 row has the technician measure the outlet water temperature with a contact thermometer and compare it with the display’s Information mode reading (the “1” in the first digit). If they are not close, a sensor is replaced, and the control module if the new sensor does not solve it (ultra-gas-series-2-control-supplement, p. 31). The row names the “return temperature sensor” at this step, although E18 is the outlet code; that is how it is printed.
• Water flow through the boiler. Step 1 of the E18 row says this should only happen when the heat demand is lower than the boiler’s lowest firing rate, such as a single small zone, and lists system checks: boiler and system full of water, no trapped air, system piping and components, piping that agrees with the boiler manual, circulator operation, and the outlet sensor’s connector and the sensor itself (ultra-gas-series-2-control-supplement, p. 31). The row for b18, the soft lockout, has the same list with pipe size and circulator capacity added (p. 26). The row for E25, a temperature rise above 58°F, refers to these suggestions as “hard lockout code 18” (p. 31).

Related codes: E19, b18, E25. All Weil-McLain codes

Weil-McLain Ultra Series 1 and 2 error code E28: blower not running

Checked October 2026

Short answer On Weil-McLain Ultra Series 1 and 2 boilers, E28 is a hard lockout for the blower: 'Blower not running' in the troubleshooting table, 'No signal from blower' in the quick-reference lists. No owner steps; a technician checks the blower, wiring and control module. See what to check

What it means

E28 is a hard lockout on Weil-McLain Ultra Series 1 and 2 boilers: the control does not get the signal it expects from the blower. The troubleshooting table calls it “Blower not running” (ultra-gas-series-2-control-supplement, p. 31), and the quick-reference lists call it “No signal from blower” (ultra-gas-series-2-control-supplement, p. 21; ultra-series-1-boiler-manual, p. 41). The display flashes the first digit, “E” and the two-digit code, and the boiler stays off until a manual reset (ultra-gas-series-2-control-supplement, pp. 21, 28).

The display has a blower check of its own. In Information mode, item 6 shows the target outlet water temperature, and if it reads 6._32, the blower has failed (ultra-gas-series-2-control-supplement, p. 20). The quick-reference list prints “Check INFO #6” beside E28 and E29 (ultra-gas-series-2-control-supplement, p. 21).

Check these first

The Ultra Series 2 user’s manual has no code list and gives the owner no steps for E28 (ultra-gas-series-2-users-manual).

1. If you smell gas, stop and follow the steps at the top of this page.
2. The boiler stays off until a manual reset (ultra-gas-series-2-control-supplement, p. 21). The Ultra Series 2 user’s manual says that if the boiler will not operate when there is a call for heat and the piping is not hot, you follow “To turn off gas to the appliance” and call your service technician or gas supplier (ultra-gas-series-2-users-manual, p. 9, step 11). The restart after a hard lockout is described in the control supplement and the Ultra Series 1 Boiler Manual, documents for installers and service technicians: the RESET button on the Ultra display panel (ultra-gas-series-2-control-supplement, pp. 9, 21; ultra-series-1-boiler-manual, p. 32).
3. Call a qualified service technician. Every step in the E28 row is a check or a replacement of the blower, its wiring or the control module (ultra-gas-series-2-control-supplement, p. 31).

When to call a licensed technician

All of E28 is technician work. The row’s steps, in order (ultra-gas-series-2-control-supplement, p. 31):

• The technician reads INFO #6 in Information mode; 6._32 means the blower has failed.
• The power supply to the blower is checked. If the blower is not getting power, the wiring is inspected, and the control module is replaced if the wiring is correct and in good condition.
• If the blower is getting power, a further test tells a failed blower from a failed control module, and that part is replaced.

Related codes: E29, E65, b65. All Weil-McLain codes

Weil-McLain Ultra Series 1 and 2 error code E37: return sensor open circuit

Checked October 2026

Short answer On Weil-McLain Ultra Series 1 and 2 boilers, E37 is a hard lockout: the return water temperature sensor reads as an open circuit. It needs a manual reset, and the sensor and wiring checks behind it are technician work. See what to check

What it means

E37 is a hard lockout on Weil-McLain Ultra Series 1 and 2 boilers: the control sees the return water temperature sensor as an open circuit (ultra-gas-series-2-control-supplement, p. 32). An open circuit means no electrical path through the sensor and its wiring, as if it were disconnected. The return sensor reads the water coming back into the boiler; the display’s Information mode shows its reading as item 2 (ultra-gas-series-2-control-supplement, p. 20).

The display flashes the first digit, “E” and the two-digit code, and the boiler stays off until a manual reset (ultra-gas-series-2-control-supplement, pp. 21, 28). The neighboring codes cover the other sensor faults: E36 is the outlet sensor open circuit, and E32 and E31 are short circuits of the return and outlet sensors (ultra-gas-series-2-control-supplement, p. 32).

Check these first

The Ultra Series 2 user’s manual has no code list and gives the owner no steps for E37 (ultra-gas-series-2-users-manual).

1. If you smell gas, stop and follow the steps at the top of this page.
2. The boiler stays off until a manual reset (ultra-gas-series-2-control-supplement, p. 21). The Ultra Series 2 user’s manual says that if the boiler will not operate when there is a call for heat and the piping is not hot, you follow “To turn off gas to the appliance” and call your service technician or gas supplier (ultra-gas-series-2-users-manual, p. 9, step 11). The restart after a hard lockout is described in the control supplement and the Ultra Series 1 Boiler Manual, documents for installers and service technicians: the RESET button on the Ultra display panel (ultra-gas-series-2-control-supplement, pp. 9, 21; ultra-series-1-boiler-manual, p. 32).
3. Call a qualified service technician. The E37 row deals only with the sensor, the wiring harness and the control module (ultra-gas-series-2-control-supplement, p. 32).

When to call a licensed technician

The whole E37 row is technician work, in this order (ultra-gas-series-2-control-supplement, p. 32):

• inspecting the return water temperature sensor and its wiring;
• replacing the sensor if the wiring is correct and in good condition;
• replacing the low voltage wiring harness if the problem persists;
• replacing the control module if the new harness does not resolve it.

Related codes: E36, E32, E31. All Weil-McLain codes

Weil-McLain Ultra Series 1 and 2 status code 3: burner on for space heating

Checked October 2026

Short answer On Weil-McLain Ultra Series 1 and 2 boilers, a 3 in the first digit is a status, not a fault: the burner is on for space heating. The digits after it show the outlet water temperature. The service guide calls it normal operation. See what to check

What it means

On the Ultra Series 1 and 2, the display’s first character is the boiler status, and the other digits are the actual (measured) outlet water temperature (ultra-gas-series-2-control-supplement, p. 17). A 3 there means “Burner on for space heating”: the boiler is firing for the heating system, as opposed to 4, which is the burner on for domestic hot water (ultra-gas-series-2-control-supplement, p. 17; ultra-series-1-boiler-manual, p. 38).

The supplement’s troubleshooting chart treats any first digit from 1 to 8 followed by the water temperature as normal operation (ultra-gas-series-2-control-supplement, p. 24). The full list of status digits, in Weil-McLain’s order (ultra-gas-series-2-control-supplement, p. 17; ultra-series-1-boiler-manual, p. 38):

Check these first

A 3 needs no action. What you can read from the display:

1. The digits after the 3 are the outlet water temperature (ultra-gas-series-2-control-supplement, p. 17).
2. After a space heating cycle the first digit can show 7: the pump stays on for a run-on of 10 seconds (ultra-gas-series-2-control-supplement, p. 17).
3. A lockout looks different. A soft lockout alternates 9 and b with a two-digit code and clears by itself when the condition is corrected or times out (ultra-gas-series-2-control-supplement, p. 17). A hard lockout flashes E with a two-digit code and needs a manual reset (ultra-gas-series-2-control-supplement, p. 21). Look those codes up in the Weil-McLain code table.

When to call a licensed technician

• Not for a 3 on its own: the supplement’s chart calls it normal operation (ultra-gas-series-2-control-supplement, p. 24).
• When the display shows a hard lockout (E and a code). Each E code’s row in the supplement lists technician checks and part replacements (ultra-gas-series-2-control-supplement, pp. 28–32).
• If you smell gas, follow the steps at the top of this page first.

Related codes: Status 4, Status 0, Status 7. All Weil-McLain codes

Weil-McLain Ultra Series 1 and 2 status code 6: burner off, temperature reached

Checked October 2026

Short answer On Weil-McLain Ultra Series 1 and 2 boilers, a 6 in the first digit means the burner is off because the temperature setting has been reached. It is a status, not a lockout. If the boiler does not restart on its own, call a technician. See what to check

What it means

On the Ultra Series 1 and 2, the first character of the display is the boiler status and the other digits are the measured outlet water temperature (ultra-gas-series-2-control-supplement, p. 17). A 6 in the first position means “Burner off because temperature setting has been reached” in both of Weil-McLain’s status lists (ultra-gas-series-2-control-supplement, p. 17; ultra-series-1-boiler-manual, p. 38).

It is one of the normal operating states. The supplement’s troubleshooting chart says that a first digit from 1 to 8 followed by the water temperature “is normal operation” (ultra-gas-series-2-control-supplement, p. 24). A lockout looks different: a soft lockout alternates 9 with b and a two-digit code, and a hard lockout flashes E with a two-digit code (ultra-gas-series-2-control-supplement, pp. 17, 21).

Check these first

1. Read the rest of the display. The digits after the 6 are the outlet water temperature (ultra-gas-series-2-control-supplement, p. 17).
2. Give the boiler time to cool. The supplement’s chart for a boiler that is not firing with a 6 in the first digit says the water may have passed the limit setting, and that the boiler will restart after the water temperature has dropped below that setting minus the differential (ultra-gas-series-2-control-supplement, p. 24).
3. If the display changes to 9 and b, or starts flashing E, the boiler has gone into a soft or hard lockout; look that code up in the Weil-McLain code table (ultra-gas-series-2-control-supplement, pp. 17, 21).
4. If the boiler stays on 6 and does not restart, call a qualified service technician. The same chart’s second possibility, a lost flame signal, is also expected to end in a restart; when it does not, the steps that follow are technician work (ultra-gas-series-2-control-supplement, p. 24).

When to call a licensed technician

The chart gives the technician two paths (ultra-gas-series-2-control-supplement, p. 24):

• Water above the limit setting (parameter 4). The boiler shut down on limit, and the chart sends the technician to the corrective actions for soft lockout code 18: boiler and system full of water, trapped air, piping, circulator operation and the outlet sensor (ultra-gas-series-2-control-supplement, p. 26).
• Water not above the limit. The control may have lost the flame signal. The technician checks the flame signal, checks gas flow, incoming gas pressure, gas line size and the gas regulator, inspects and cleans the ignition electrode and its wiring, and if the problem persists services the burner with the boiler’s maintenance kit.

Related codes: Status 3, Status 0, b18. All Weil-McLain codes

Weil-McLain AquaBalance error code A01: no burner ignition

Checked October 2026

Short answer On Weil-McLain AquaBalance Series 2 boilers, A01 means no burner ignition after five attempts; the Series 1 manual calls it 'Lockout indication'. The user's manuals give the owner no reset and no steps for A01. Call a technician. See what to check

What it means

A01 is an “A” code on the Weil-McLain AquaBalance: a lockout that stops the boiler until it is reset by hand (aquabalance-series-2-boiler-manual, p. 92). The Series 2 boiler manual words it “No burner ignition after five attempts” (aquabalance-series-2-boiler-manual, p. 92). The Series 1 manual’s code list says only “Lockout indication”, and its cause table names the fault “No burner ignition” (aquabalance-boiler-manual, pp. 88–89). When a fault occurs, the display flashes together with the fault symbol and shows the code (aquabalance-series-2-boiler-manual, p. 92).

The AquaBalance also has a status code for failed ignition tries. D3 means the boiler has made 3 tries for ignition and failed, and a re-trial delay is in effect for 3 more tries (aquabalance-series-2-boiler-manual, p. 68). The boiler manual’s numbers do not agree with each other: its ignition-safety test says the boiler tried to ignite three times (d3) before the A01 lockout (p. 83), and its sequence of operation says the boiler goes into lockout A01 after 5 attempts (p. 90).

Check these first

The AquaBalance user’s manuals give no reset procedure and no steps for A01. The one owner item below, the condensate drain check, comes from the user’s manuals.

1. If you smell gas, stop and follow the steps at the top of this page.
2. Look at the condensate drain. The user’s manual has the owner inspect the condensate drain tubing and the end of the tube, inspect the trap under the boiler, check it for sediment and clean it out if necessary, make sure it has water in it, and contact a boiler service technician about any problem. A trap with no water inside means contacting a boiler service technician immediately (aquabalance-series-2-user-manual, p. 8; the Series 1 manual says the same, aquabalance-series-1-user-manual, p. 8). A blocked condensate trap, or a drain hose looped so that it makes a second trap, is one of the A01 causes in the boiler manual (aquabalance-series-2-boiler-manual, p. 93).
3. The reset is described only in the boiler manual, which is for use only by the qualified installer or service technician (aquabalance-series-2-boiler-manual, p. 2), and in the Quick Start Guide. The user’s manuals only name the “Reset / OTC button” (aquabalance-series-2-user-manual, p. 11). The boiler manual says an A code is cleared with the RESET button on the front panel (1 second), at most 5 resets in 24 hours, and “Do not leave the boiler operating without a complete diagnosis.” (aquabalance-series-2-boiler-manual, p. 92). The Quick Start Guide gives 1.5 seconds (aquabalance-control-module-quick-start-guide, p. 13).
4. If A01 comes back, call a qualified service technician.

When to call a licensed technician

On a new installation, the Quick Start Guide says to have the contractor verify that the gas supply is purged (aquabalance-control-module-quick-start-guide, p. 13).

The A01 cause table in the boiler manual lists these checks, all of them technician work (aquabalance-series-2-boiler-manual, p. 93):

• No gas: check the gas flow to the boiler and that the air has been eliminated from the pipes.
• The ignition/detection electrode: its wiring, position and deposits, and whether it is deformed or misaligned or has the wrong gap (5/32”).
• Combustion: a combustion test for natural gas or LP per the manual’s charts.
• The gas valve, replaced if necessary, and the gas supply pressure.
• The condensate trap, checked and cleaned. The same row adds: “Also inspect gas valve, blower, venturi, igniter, and heat exchanger, and replace those with signs of damage.”

The Quick Start Guide adds a dirty heat exchanger overdue for cleaning and maintenance to the list, and gives the gas supply pressure spec as “3.5 to 11 w.c.” (aquabalance-control-module-quick-start-guide, p. 13). Its ignitor gap check starts by shutting off the gas supply and removing the ignitor; that is service work, not an owner task (aquabalance-control-module-quick-start-guide, p. 15).

Related codes: A06, A02, D3. All Weil-McLain codes