HTP Boiler Error Codes: 10, 11, 29 and 501 Explained

By Ray Bennett · Updated 17 October 2026 · 9 min read · Checked against the sources at the end

HTP Boiler Error Codes: 10, 11, 29 and 501 Explained

Short answer

HTP's 2020 UFT chart calls Er:10 repeated flame loss, Er:11 failed ignition and Er:29 an open air pressure switch circuit. Elite Ultra uses a different chart: 501 means no flame detected after three attempts. Match the model and manual edition before using a code list.

HTP boiler error codes need the boiler model beside them: HTP’s UFT chart uses Er:11 for failed ignition, while the Elite Ultra chart below uses 501. A number copied from another HTP range can send you toward the wrong repair.

Start with the full display message and the model on your paperwork or an accessible identification label. This guide covers the UFT and Elite Ultra versions named below, with owner checks kept outside the cabinet.

Before you start

What to carry: a torch, your phone and the boiler’s manual. Photograph the display, model and serial number. Include whether the trouble started during heating, hot water use or after a power interruption.

Gas or electric? HTP’s manuals here cover gas fired water boilers. These tables do not cover electric boilers, oil burners, or every product sold under the Elite name.

Renting? Send those details to whoever arranges your heating repairs before authorising work.

Deal with danger before the code.
Overheating or gas that will not shut off. HTP’s UFT and Elite Ultra installation manuals say to close the manual gas control valve. HTP’s UFT Er:16 sequence runs the pumps and fan to cool the heat exchanger. Do not interrupt that cooling sequence. Arrange urgent service.

A smell of gas. HTP says not to light an appliance, touch electrical switches or use a phone inside the building. Leave and call the gas supplier from outside; follow its instructions, and call the fire department if you cannot reach it.

A carbon monoxide alarm. CPSC says to move outside to fresh air, call 911 or the fire department, and account for everyone. Stay out until emergency responders allow you back. If the boiler caused the alarm, it needs trained personnel to service it before reuse.

Flooding or internal work. HTP says not to use these boilers if any part has been under water. Its manuals reserve repairs for qualified service technicians. Keep covers fitted and leave gas pressure tests, ignition parts, wiring and safety switches to the repairer.

Elite Ultra owners: check the recall first

CPSC’s June 2025 HTP recall covers certain ELU-150WBN and ELU-199WBN boilers. Incorrect burner door studs can prevent a proper seal, allowing flames and gases to escape. CPSC identifies fire and carbon monoxide hazards.

Use the complete model and serial ranges in that notice. They are wider than the ranges on HTP’s March safety page. CPSC says the rating plate is on the boiler’s left side and tells owners of recalled units to stop using them and contact HTP for a repair at no cost.

The recall is a separate check from the error number. Have HTP confirm whether your unit is affected and whether any required repair has already been completed.

Choose the matching HTP control

Two different HTP code families. These are simplified display examples, not exact control layouts.

Check 1No parts needed to identify the boiler

Match the model and manual edition

UFT: the table here follows HTP’s LP-542, dated June 9, 2020. Its cover specifies UFT-80, 100, 120, 140, 175 and 199 floor or wall models manufactured on or after January 1, 2020. The control flashes Er followed by a number.

Elite Ultra: the second table follows HTP’s 420011303900 installation manual for ELU-150WBN, ELU-199WBN and ELU-199WCN. HTP identifies its control as GALEVO2 with an LCD display. The printed revision is February 28, 2022, despite the date in the download filename.

HTP lists a separate UFT manual for boilers made before 2020 and another Elite Ultra manual for smaller models. Earlier UFT units, UFT combis, Elite FT, Elite Plus, Mod Con and other controls need their own matching charts.

UFT error codes 10, 11 and 29

These meanings come from HTP’s 2020 UFT table. The distinction between losing a flame and failing to light helps explain what the technician will investigate.

UFT display	Meaning in HTP’s 2020 manual	What the technician investigates
Er:10	Flame extinguished five times	Gas supply, flame sensing, wiring, vent openings and flame stability
Er:11	Ignition failed five times	Gas supply, flame sensing, igniter connections and the spark igniter
Er:16	Central heating supply water temperature too high	Water flow, temperature sensors and control settings
Er:20	Condensate drain trap switch circuit open	Switch, hose, wiring, condensate drainage and exhaust blockage
Er:28	Overheat sensor open or shorted	Sensor, connections and control
Er:29	Air pressure switch circuit open when it should be closed	Switch, hose, wiring, condensate drainage and exhaust blockage
Er:31 / Er:33 / Er:35	Return / central heating / exhaust temperature sensor open or shorted, respectively	The named sensor and its connections
Er:41 / Er:61	Fan speed too high with flame on / abnormal fan speed feedback, respectively	Fan operation, wiring and controls; vent blockage for Er:41
Er:42	Low water cutoff circuit open	The installed cutoff circuit and its wiring
Er:80 / Er:81	Repeated low water level detection / low water level circuit fault, respectively	Water level, leaks, trapped air, sensor and wiring
Er:94	Exhaust sensor detects vent temperature above 190 degrees F	Sensor, exhaust blockage and control settings

Check 2A service visit; parts depend on the test results

Er:10 or Er:11: separate flame loss from failed ignition

For both faults, HTP’s 2020 UFT chart allows an automatic reset after one hour, up to three times. That explains why an apparently stopped boiler may attempt to run again. It does not mean the underlying trouble has been repaired.

HTP’s Er:11 checks include the igniter transformer connection and a damaged or dirty spark igniter. Its Er:10 branch also checks the vent openings and whether the flame stays stable. Both branches include gas pressure and flame detection, so neither code identifies one part to buy.

Tell the repairer whether you heard repeated attempts to start or the boiler ran before stopping. There is no need to open the burner compartment to collect that information.

Check 3No parts for an accessible obstruction; service for an unresolved fault

Er:29: check the vent path before considering a reset

For this UFT, HTP’s warning names Er:29, Er:41, Er:42 and Er:94: turn off the gas valve at the manual shutoff, then check the vent terminations for obstructions. Its UFT owner manual also names Er:20 in its blocked vent warning.

Look only at openings safely accessible from the ground. HTP’s UFT owner instructions allow removal of debris from the openings but exclude difficult to reach locations. Leave fixed pipes connected, do not touch the exhaust pipe, and keep tools out of the boiler.

HTP permits a Power button reset when no obstruction is found, and calls for a technician or gas supplier if the error continues. If you cannot confidently follow your own model’s shutdown and restart instructions, leave the gas off for that visit.

The Er:29 repair list includes the condensate drain as well as the air pressure switch. A clear outside opening does not rule out an internal hose, drain or wiring problem. Never bridge the switch to make the boiler run.

HTP's UFT Er:29 checks span venting, condensate drainage and the pressure switch circuit. Only the accessible outside openings are an owner check here.

Check 4A gas service visit to test ignition and combustion

501: the control did not detect a flame

For ELU-150WBN, ELU-199WBN and ELU-199WCN, HTP defines 501 as no flame detected after three attempts. Its chart includes gas supply problems, blocked intake or exhaust, a blocked condensate drain, ignition faults, combustion settings and flame sensing.

Those checks explain why an igniter replacement alone may not solve it. HTP specifically requires a qualified technician with a combustion analyzer for combustion adjustments. Leave those settings and the gas valve alone.

HTP’s same chart distinguishes 504, flame lost ten times during operation, from 501. It also lists 5P1, 5P2 and 5P6 for the first, second and third failed ignition attempts. Keep the P when reporting one of those warnings.

The following are selected entries from that Elite Ultra manual, not UFT meanings. HTP labels both automatic and manual reset faults as blocking in this installation chart, so the reset type matters more than that word alone.

Elite Ultra display	Meaning in HTP’s chart	Reset type listed
108	Water pressure too low	Automatic after the condition is corrected
110 / 112	Supply / return temperature sensor circuit open or shorted, respectively	Automatic
501	No flame detected after three attempts	Manual
502	Flame detected out of sequence	Automatic
504	Flame lost ten times during operation	Manual
602	Exhaust temperature exceeded 204 degrees F; cannot clear until below 149 degrees F	Manual
603	Blocked condensate switch open	Manual
605	Exhaust temperature sensor circuit open or shorted	Automatic
612	Blower did not reach the required speed	Manual

When a reset is not the next step

Check 5Diagnosis first; the cause decides the repair work

Use the owner's response to the fault

For Elite Ultra 108, HTP’s user manual tells the owner to switch off the boiler and external electrical supply, close the main gas valve, and contact a qualified technician to check for water leaks. It does not give the owner a filling procedure.

For an Elite Ultra lockout that returns after a reset, HTP gives that same shutdown and service instruction. The overheating and gas emergency rules above come first. Repeated button presses are not a repair.

For UFT Er:80 or Er:81, HTP’s service chart includes leaks, water supply and sensor checks. Report any visible leak and the gauge reading. Our boiler pressure guide explains the wider investigation without treating every water fault as a reason to add water.

After the repair, watch whether heat returns to the rooms and whether the fault stays cleared. HTP’s UFT owner manual calls for checking proper operation with the service technician after servicing. If the code clears but the house stays cold, use boiler not working for the next checks.

What each one takes

Finding	Work involved
Wrong code chart	Matching the model, manufacture date and control before buying parts
UFT Er:10 or Er:11; Elite Ultra 501 or 504	Testing fuel supply, ignition, flame sensing and the relevant air or drain paths
UFT Er:29 or Elite Ultra 603	Finding the blockage or circuit fault before replacing a switch
Water level, pressure or temperature fault	Checking leaks, circulation, sensors and installed controls
Elite Ultra 612	Checking blower wiring, blower operation and the control signal
Affected Elite Ultra recall unit	Arranging HTP’s recall repair with a certified technician

Questions people ask

Why does my HTP fan run when the burner is off?

HTP’s UFT owner manual says the fan continues after the burner stops to clear combustion gases from the exhaust. It may also run for freeze protection. Fan noise alone does not identify a fault; use any displayed code and whether the boiler is heating.

What does UFT Er:72 mean?

HTP’s 2020 UFT chart calls it a flame signal detected before ignition. Its checks include an unsecured cover allowing external light to reach the flame sensor, sensor connections and the control. Keep the cover fitted and leave that investigation to the technician.

Why is UFT Er:77 showing while the boiler still heats?

HTP defines Er:77 as a shorted outdoor sensor. Its 2020 UFT manual says the boiler still operates at the maximum setting of its outdoor reset curve during this fault. Heating continuing does not mean the sensor fault has cleared.

Does Elite Ultra 619 mean a broken blower?

No. For the three Elite Ultra models covered here, HTP calls 619 a power limiting mode during new startup. Its manual says normal operation returns after five uninterrupted minutes of burner operation in heating or hot water mode. The blower speed fault in this chart is 612.

What if my display or model is not listed?

Use HTP’s manual library to find the document for the full model and manufacture date. A missing code here does not make it harmless. Send the complete message to your heating repairer, especially if the boiler has stopped heating.

The other boiler guides: boiler keeps turning off, boiler not working, boiler pressure, and Burnham Alpine boiler error codes.

Sources: HTP UFT Installation Manual LP-542 Rev. 002 Rel. 001, 6.9.20, pp. 1, 6, 56 to 58; UFT User's Information Manual LP-543, 12.15.15, pp. 1, 4, 7 to 9; Elite Ultra Installation Manual 420011303900, printed revision 2.28.22, specifications and pp. 79, 83 to 85; Elite Ultra User's Information Manual 420010970100 / LP-699, 6.11.20, pp. 1, 3 to 5; HTP UFT and Elite Ultra document pages and ELU safety notice; CPSC recall 25-325, June 5, 2025, and Carbon Monoxide Questions and Answers.