Slant/Fin error codes — full list with meanings | TroubleAtlas

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HVAC Error Codes · Manufacturer index

Slant/Fin error codes

The complete list of Slant/Fin fault codes shown on the display, each with what it means and the page that explains how it is diagnosed and fixed.

137documented codes
137with documented causes
Slant/Fin boiler with the fault code shown on the display
Quick Answer

Slant/Fin heating appliances display 137 documented error codes. Each code below opens its own page with the official meaning, the documented causes, the safety assessment and the parts involved.

01

All Slant/Fin Error Codes

137 codes, each with its own page. Click a code to open the meaning, the documented causes and the repair.

CodeWhat it means
101Exchanger sensor fault
105Flame detected out of sequence
106Flame lost in MFEP
107Flame lost early in run
108Flame lost in run
110Ignition failure occurred
111Flame current lower than WEAK threshold
112Pilot test flame timeout
113Flame circuit timeout
115Fan was limited to its minimum duty cycle
119Controller interaction communications fault
129Fan speed failed during pre-ignition
131Fan movement detected during standby
143Internal fault: Flame bias out of range 1
144Internal fault: Flame bias out of range 2
145Internal fault: Flame bias out of range 3
146Internal fault: Flame bias out of range 4
147Internal fault: Flame bias out of range 5
148Internal fault: Flame bias out of range 6
150Flame not detected
154Purge fan switch ON
155Purge fan switch OFF
156Combustion pressure and Flame ON
157Combustion pressure and Flame OFF
166Outlet sensor type was invalid for DHW
184Invalid BLOWER/HSI output setting
189Invalid Flame sensor type setting
192Invalid Igniter on during setting
194Invalid Ignite failure response setting
195Lead Lag backup modulation sensor setting was invalid
196Invalid Ignition source setting
202Invalid Main Flame Establishing Period time setting
204Invalid NTC sensor type setting
206Invalid Pilot Flame Establishing Period setting
21Internal fault: Flame number of sample mismatch
212Invalid Pre-ignition time setting
216Invalid Run flame failure response setting
219Using backup Lead Lag header sensor due to sensor failure
229Lead Lag slave communication timeout
232Invalid Pressure sensor type setting
243Invalid UV with spark interference not compatible with Igniter on throughout
25Internal fault: Spark voltage changed too much during flame sensing time
253Lead Lag modulation sensor not valid with setpoint source
255Lead Lag modulation sensor not valid with local modulation source
259Modulation output must be fan if controller interaction is enabled
261Neighbor burner control blower fault detected
27Internal fault: Flame rod shorted to ground detected
272Abnormal Recycle: Pressure sensor fault
274Abnormal Recycle: Demand off during Pilot Flame Establishing Period
278Abnormal Recycle: LCI off during Pre-Ignition test
279Abnormal Recycle: LCI off during Pre-Ignition time
280Abnormal Recycle: LCI off during Main Flame Establishing Period
281Abnormal Recycle: LCI off during Ignition period
285Abnormal Recycle: Demand off during Pre-Ignition test
286Abnormal Recycle: Demand off during Pre-Ignition time
287Abnormal Recycle: Flame was on during Safe Start check
288Abnormal Recycle: Flame was on during Drive to Purge Rate
289Abnormal Recycle: Flame was on during Measured Purge Time
29Internal fault: Flame bias cannot be set in range
290Abnormal Recycle: Flame was on during Drive to Light off Rate
291Abnormal Recycle: Flame was not on at end of Ignition period
292Abnormal Recycle: Flame was lost during Main Flame Establishing Period
293Abnormal Recycle: Flame was lost early in Run
294Abnormal Recycle: Flame was lost during Run
296Abnormal Recycle: Interrupted air flow switch was off during Drive to Purge Rate
297Abnormal Recycle: Interrupted air flow switch was off during Measured Purge Time
298Abnormal Recycle: Interrupted air flow switch was off during Drive to Light off Rate
299Abnormal Recycle: Interrupted air flow switch was off during Pre-Ignition test
300Abnormal Recycle: Interrupted air flow switch was off during Pre-Ignition time
301Abnormal Recycle: Interrupted air flow switch was off during Main Flame Establishing Period
302Abnormal Recycle: Ignition failed due to interrupted air flow switch was off
306Abnormal Recycle: ILK off during Pre-Ignition test
307Abnormal Recycle: ILK off during Pre-Ignition time
308Abnormal Recycle: ILK off during Main Flame Establishing Period
309Abnormal Recycle: ILK off during Ignition period
31Internal fault: SLO electronics unknown error
311Run was terminated due to interrupted air flow switch was off
313Run was terminated due to fan failure
314Abnormal Recycle: Fan failed during Drive to Purge Rate
315Abnormal Recycle: Fan failed during Measured Purge Time
316Abnormal Recycle: Fan failed during Drive to Light off Rate
317Abnormal Recycle: Fan failed during Pre-Ignition test
318Abnormal Recycle: Fan failed during Pre-Ignition time
319Abnormal Recycle: Fan failed during Ignition period
320Abnormal Recycle: Fan failed during Main Flame Establishing Period
324Abnormal Recycle: Hardware flame bias
325Abnormal Recycle: Hardware static flame
326Abnormal Recycle: Hardware flame current invalid
327Abnormal Recycle: Hardware flame rod short
330Abnormal Recycle: Hardware SLO flame ripple
331Abnormal Recycle: Hardware SLO flame sample
332Abnormal Recycle: Hardware SLO flame bias range
333Abnormal Recycle: Hardware SLO flame bias heat
336Abnormal Recycle: Hardware SLO static flame
352Abnormal Recycle: fault stack sensor
355Abnormal Recycle: fault outlet sensor
357Abnormal Recycle: fault DHW sensor
359Abnormal Recycle: fault inlet sensor
374Abnormal Recycle: Hardware flame bias high
375Abnormal Recycle: Hardware flame bias low
376Abnormal Recycle: Hardware flame bias delta high
377Abnormal Recycle: Hardware flame bias delta low
378Abnormal Recycle: Hardware flame bias dynamic high
379Abnormal Recycle: Hardware flame bias dynamic low
380Abnormal Recycle: Fan Speed Not Proven
381Abnormal Recycle: Fan Speed Range Low
382Abnormal Recycle: Fan Speed Range High
383Abnormal Recycle: Pre-Ignition test failed, recycle
448Flame too low
449Modulation rate was limited due to flame strength
451Circulation pump control was invalid
452Circulation pump P-gain was invalid
453Circulation pump I-gain was invalid
454Circulation pump temperature was invalid
455Circulation pump outlet temperature was invalid
456Circulation pump inlet temperature was invalid
457Circulation pump outlet temperature was invalid
458Circulation pump sensor choice was invalid
459Circulation pump PID setpoint was invalid
463Demand lost in run due to no flame
47Flame rod to ground leakage
4924VAC voltage low/high
62Fan speed not proved
622Lead Lag modulation sensor was not valid with setpoint source
623Lead Lag modulation sensor was not valid with local setpoint source
624Lead Lag modulation sensor was not valid with local modulation rate source
67Fan off cycle rate was invalid, % vs
69Modulation was over ridden due to sensor fault
72Flame strength rate differential was invalid
73Flame strength step rate was invalid
75Absolute max fan speed was out of range
76Absolute min fan speed was out of range
77Fan gain down was invalid
91Inlet sensor fault
93DHW sensor fault
95Stack sensor fault
96Slow start was ended due to outlet sensor fault
02

What Fails Most Often on Slant/Fin

Grouped from the official meaning of each of the 137 codes above — not from opinion. The number is how many different fault codes point at that component.

ComponentCodesExamples
Ignition69106, 107, 108, 110
Fan24115, 129, 131, 154
Temperature Sensor19101, 166, 195, 204
Pump9451, 452, 453, 454
Pressure Switch7296, 297, 298, 299
False Flame3105, 157, 290
Communication2119, 229
Dhw Sensor2357, 93
03

Parts & Prices

Search Slant/Fin replacement parts…

The parts most often involved in the Slant/Fin faults listed above.

Ignition / spark electrode
OEM Part · Slant/Fin
Check price View price
Fan / blower assembly
OEM Part · Slant/Fin
Check price View price
Temperature sensor (NTC)
OEM Part · Slant/Fin
Check price View price
Circulating pump
OEM Part · Slant/Fin
Check price View price
Compatible Ignition / spark electrode
Compatible · Generic
Check price View price
Compatible Fan / blower assembly
Compatible · Generic
Check price View price
Compatible Temperature sensor (NTC)
Compatible · Generic
Check price View price
Compatible Circulating pump
Compatible · Generic
Check price View price
Reconditioned Ignition / spark electrode
Used / Tested · Slant/Fin
Check price View price
Reconditioned Fan / blower assembly
Used / Tested · Slant/Fin
Check price View price
Reconditioned Temperature sensor (NTC)
Used / Tested · Slant/Fin
Check price View price
Reconditioned Circulating pump
Used / Tested · Slant/Fin
Check price View price
View All Slant/Fin Parts →

Prices and availability vary by region and are shown by the retailer, not by TroubleAtlas.

04

Diagnostic Tools

What an engineer uses to work through the codes on this page.

Digital Multimeter (TRUE RMS)

For testing electrode resistance and PCB voltages

$35–$80 View price

Gas Leak Detector

Essential for checking connections after any gas valve work

$25–$45 View price

Manometer / Pressure Gauge

To measure gas inlet and burner pressure

$40–$90 View price

Combustion Analyzer

For verifying flue gas readings after repair

$180–$350 View price
Full HVAC diagnostic toolkit
Shop all diagnostic tools →
05

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Considering a New Heating System

Considering a New Heating System?

If your Slant/Fin appliance is over 10 years old, replacing it with a modern condensing boiler or air-source heat pump could cut energy bills and remove the recurring faults listed on this page.

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Written by TroubleAtlas Technical Team · Last updated: 2026-08-02 · Sources: manufacturer service documentation · How we verify
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