Weil-McLain Boiler Error Codes: Messages and Fixes

By Ray Bennett · Updated 23 October 2026 · 9 min read · Checked against the maker’s manual

Weil-McLain Boiler Error Codes: Messages and Fixes

Short answer

Weil-McLain's Ultra Series 4 and WM97+ Series 2 manuals use named faults; the GV90+ uses flashing lights. IGNITION FAULT means five tries without detecting flame on those Ultra and WM97+ models. FLAME FAULT means flame detected when none should be present. Match the model before choosing a fix.

Weil-McLain boilers report a fault in one of two ways. The Ultra Series 4 and the WM97+ Series 2 show a message such as IGNITION FAULT on their display, while the GV90+ flashes a set of lights on its control, so the meaning depends on your model.

This page covers Ultra Series 4, WM97+ Series 2 and GV90+. It explains the messages in those manuals, the checks you can make outside the boiler and what the repair visit involves. It does not give a number code chart for earlier Ultra controls, ECO Tec, Evergreen or AquaBalance.

Before you start

What to carry: a torch, a pen and your boiler’s user manual. Leave the cabinet closed for these checks.

Gas or electric? All three Weil-McLain manuals here cover gas fired hot water boilers. An oil burner control or an electric boiler needs its own fault list.

Keep the whole message. Write down the model, series, exact wording and what was happening when the heat stopped. For lights, record every flashing label and whether they flash together or alternate.

Renting? Send those details to the landlord or whoever arranges heating repairs before authorising work.

Deal with danger before the code.
Overheating, or gas that will not shut off. Weil-McLain’s Ultra and GV90+ instructions say to leave the boiler’s electrical supply on and shut off the gas at a valve outside the appliance. Do not use a power reset in that situation. Arrange urgent service.

Smell gas? Weil-McLain’s Ultra user manual says not to light an appliance, touch an electrical switch or use a phone inside. Leave and call the gas supplier from outside; call the fire department if the supplier cannot be reached.

FLAME FAULT is a service call. On Ultra Series 4 and WM97+ Series 2, Weil-McLain defines it as flame detected when none should be present. Its checks include combustion testing and whether the gas valve closes properly. Leave those tests and the restart to a qualified heating technician.

No internal repairs here. Weil-McLain reserves the Ultra boiler service manual for qualified installers and technicians. Do not bridge a safety switch, adjust a gas valve or unplug sensors to get heat back.

Match the message to the boiler

Match the model and the display together. These are simplified examples, not pictures of the control panels.

Check 1No parts to buy for this check

Choose the right chart

Ultra Series 4: Weil-McLain calls its control U-Control. Use the Ultra message table below.

WM97+ Series 2: use its separate table, even when the wording matches the Ultra. Weil-McLain gives these boilers different reset conditions for some faults.

GV90+: Weil-McLain’s integrated boiler control uses POWER, TSTAT CIRC, LIMIT, PRESS SWITCH and FLAME lights. Steady lights show its normal sequence; flashing combinations identify problems.

Looking for E02, E 04 or E18? Those number codes are outside the manuals used for this page. Use the fault chart supplied for your exact boiler and control. Do not turn an E code into a similarly named fault from the tables below.

Ultra Series 4: what the messages mean

Weil-McLain’s Series 4 troubleshooting chart gives the meanings below. The last column describes the technician’s investigation, not a list of parts to buy.

Ultra Series 4 message	What Weil-McLain means	What the technician checks
IGNITION FAULT	Five ignition attempts without detecting flame	Condensate trap, igniter, burner, gas pressure, combustion and vent restrictions
FLAME FAULT	Flame detected when it should not be present	Combustion and gas valve shutoff, as described in the warning above
TEMP RISE TOO QUICKLY	Supply temperature rises faster than 2 degrees F per second during the first two minutes of firing	Piping, circulator sizing and sensor connections
SUPPLY 58F > RETURN	Boiler outlet is more than 58 degrees F hotter than the inlet while firing	Piping arrangement, circulator sizing and sensor connections
RETURN > SUPPLY	Return temperature is at least 10 degrees F above supply; system sensors must show this for 10 minutes	Pump direction and system sensor placement
TEMPERATURE SENSOR	An open or shorted sensor, or dual sensor readings more than 10 degrees F apart	Which sensor is affected, its wiring and resistance
FLUE TEMP TOO HIGH	Flue sensor reading above 216 degrees F	Sensor, heat exchanger and vent condition; technical support
LOW WTR CUTOFF OPEN	Low water cutoff contacts open for more than one second	Water level first, then cutoff wiring if water is not low
LIMIT OPEN	An external manual or automatic reset limit has opened	Why the safety device opened and its wiring
HIGH TEMP LIMIT	Boiler sensor reached the high limit setting	Isolation valves, pump programming, piping and circulation
BLOWER FAULT	Blower cannot reach the required speed, or reports rotation when off	Wiring, speed feedback and electrical supply
DISPLAY COMM	Display communication lost for 30 seconds	Connections between the screen and control
GAS VALVE FAULT	Problem in the control’s gas valve output circuit	Valve wiring and control

A pressure switch or expansion board message? Weil-McLain also lists AIR PRESSURE SW FAULT, GAS PRESSURE SW FAULT, HW FAULT EXPANSION BRD, GV FAULT EXPANSION BRD and EXP BOARD COM FAULT. Its chart says residential Ultras do not use those switches or an expansion board and directs the technician to verify the selected boiler size. Do not buy a pressure switch from that wording alone.

WM97+ Series 2: use its own fault list

Weil-McLain’s WM97+ Series 2 chart includes these messages. The tank sensor rows apply only to an Aqua Logic companion water heater installation.

WM97+ Series 2 message	What Weil-McLain means
IGNITION FAULT	Five ignition attempts without detecting flame
FLAME FAULT	Flame detected when none should be present
TEMP RISE TOO QUICKLY	Supply temperature rises faster than 2 degrees F per second in the first two minutes of firing
SUPPLY 58F > RETURN	Boiler outlet is more than 58 degrees F above inlet temperature
RETURN > SUPPLY	Return temperature is at least 10 degrees F above supply
TEMPERATURE SENSOR	Sensor shorted or disconnected, or dual readings more than 10 degrees F apart with the burner on
FLUE TEMP TOO HIGH	Flue sensor reading above 216 degrees F
LOW WTR CUTOFF OPEN	Internal low water cutoff contacts have opened
LIMIT OPEN / HIGH TEMP LIMIT	External limit opened / boiler sensor reached the high limit setting
BLOWER FAULT	Blower misses the required speed or does not reach zero when off
GAS VALVE FAULT	Problem with the control’s gas valve output circuit
DISPLAY COM	Display communication lost for 30 seconds
TANK SENSOR FAULT, TOP or BOTTOM	Upper or lower Aqua Logic tank sensor shorted or disconnected

GV90+: which lights are flashing?

Check 2A service call if repair is needed

Read the combination, not just one lamp

Weil-McLain’s GV90+ manual gives these as the usual meanings of the light patterns. Pay particular attention to whether POWER is flashing too: LIMIT alone and POWER with LIMIT have different meanings.

GV90+ flashing lights	What Weil-McLain’s chart points to
POWER alone	Reversed polarity of the electrical supply
POWER and TSTAT CIRC	Stray voltage on thermostat wiring, or return water not reaching 140 degrees F within 20 minutes
POWER and LIMIT alternating	Limit circuit failed to stop overheating; return sensor detected water above 235 degrees F
POWER and PRESS SWITCH	Pressure switch closed when it should not be, or failed to close within five minutes of blower startup
POWER and FLAME	Three unsuccessful ignition attempts or flame sensed when it should not be there; grounding may be faulty
TSTAT CIRC alone	Return water below 40 degrees F; both internal pumps run until it warms
LIMIT alone	Open or shorted return temperature sensor

The manual places the last two patterns under nonlockout modes. For POWER and LIMIT alternating, use the overheating warning above, not a routine reset.

The owner check, and what a reset can do

Check 3No parts for removable debris; service if the fault remains

Look at the accessible air and vent openings

For the Ultra Series 4, Weil-McLain’s user manual allows you to remove an air or vent blockage only when it is easily accessible and removable. Look from a safe position on the ground. Do not dismantle vent pipes or reach into the boiler.

If the opening is clear, the obstruction cannot be removed safely, or the boiler still will not run correctly, its instructions call for a technician to inspect the boiler and vent system.

For IGNITION FAULT, Weil-McLain’s Ultra and WM97+ service charts also name a blocked condensate trap, igniter trouble, gas pressure and combustion checks. Leave those checks to a qualified heating technician rather than repeatedly resetting the boiler. For the wider symptom, see a boiler that keeps turning off.

Weil-McLain gives these two messages different meanings on Ultra Series 4 and WM97+ Series 2. The word before FAULT matters.

Check 4Service and parts depend on the fault

Let the fault decide the reset

Ultra Series 4. Weil-McLain’s user manual shows MANUAL RESET on the U-Control display. Its service chart says IGNITION FAULT retries automatically after one hour; TEMP RISE TOO QUICKLY resets after a minute, but needs manual reset after five automatic resets during the same priority heat demand.

WM97+ Series 2. Weil-McLain also gives IGNITION FAULT a one hour automatic retry. For LOW WTR CUTOFF OPEN, its chart allows automatic reset when the contacts are open for at least one but less than five seconds, and requires manual reset when open longer than five seconds. The Ultra Series 4 cutoff row instead requires manual reset.

GV90+. Weil-McLain describes a reset by interrupting power or turning down all thermostats for 45 seconds, then restoring power and the heat call. Its overheating lockout has separate requirements. That is a service decision after the overheating cause is corrected, not permission to cut power to an overheating boiler.

After it restarts. Check whether the rooms warm up and whether the same message returns. Give the repairer your record if it does. Weil-McLain’s Ultra diagnostics retain the last three lockouts with operating information, so the technician has more to inspect than the current screen.

What each one takes

Finding	What the work involves
Accessible debris at an Ultra vent opening	An owner check within the limits above, then service if heat does not return
Ignition or unexpected flame fault	A heating technician checking the ignition, fuel and combustion system
Fast temperature rise or high limit	Checking circulation, piping and controls before deciding which part needs work
Sensor, wiring or display fault	Electrical testing and a part only if the tests identify one
Low water cutoff open	Finding a water problem or a cutoff circuit fault, rather than bypassing the protection

Questions people ask

Does a red Ultra display always mean a lockout?

No. Weil-McLain’s Series 4 manual also uses a red display for a maintenance reminder. Read the words on the screen; a colour alone does not identify the fault.

Why does my Ultra show WWSD with no heat?

Weil-McLain calls this warm weather shutdown. With an outdoor sensor installed, Series 4 stays in standby for space heating when the outdoor temperature exceeds its WWSD setting. The manual says it does not stop domestic hot water operation.

Does OPEN beside an Ultra sensor mean it is broken?

Not necessarily. Weil-McLain says unused optional OUTDOOR TEMP, SYSTEM SUPPLY and SYSTEM RETURN sensors show OPEN on Series 4. An installed sensor showing OPEN needs investigation.

Can a working boiler have a blank screen?

Yes. Weil-McLain’s Ultra Series 4 troubleshooting chart includes a blank display while the boiler still operates, pointing to lost communication between the control and display. Report whether the boiler is running when you arrange service.

Does HIGH TEMP LIMIT tell me to replace the pump?

No. Weil-McLain’s Ultra Series 4 checks include isolation valves, circulator programming, piping, pump sizing and sensor connections. The message alone does not select a replacement part. See boiler circulator pump problems for that part of the investigation.

The other boiler guides: boiler not working, boiler pressure, and boiler keeps turning off.

Sources: Weil-McLain Ultra Series 4 Boiler Manual 550-100-440/1025, pp. 32, 94, 118 to 123; Ultra Series 4 User's Information Manual 550-100-441/1025, pp. 1 to 3, 6, 12; WM97+ Series 2 Boiler Manual 550-142-204/0119, pp. 112 to 115; GV90+ Boiler Manual 550-142-054/1211, pp. 2, 4, 77.