Most Common Pool Heater Error Codes in 2026: Search Data Report

Every pool tech has a heater error code burned into their memory. But which codes come up most often across the entire industry?

We analyzed over 12,500 troubleshooting searches on PoolDial from February through May 2026 to find out. The data covers every major heater brand and model, from Pentair MasterTemp gas heaters to Hayward HeatPro heat pumps.

Here is what techs are searching for most, and what it tells us about field service in 2026.

The numbers above set the stage. Gas heaters dominate error code searches by a wide margin, and Pentair models account for more than three-quarters of all heater troubleshooting traffic. Below, we break down the data by error code, brand, and fuel type.

Top 15 Pool Heater Error Codes by Search Volume

We ranked every heater error code by how often pool techs searched for it. The top 15 account for roughly 85% of all heater error searches on our platform.

Rank	Error Code	Equipment	What It Means	Searches
1	ERR SFS	Pentair MasterTemp / Max-E-Therm	Stack flue sensor detected high exhaust temperature	2,319
2	ERR AGS	Pentair MasterTemp / Max-E-Therm	Automatic gas shutoff triggered	1,883
3	ERR PS	Pentair MasterTemp / Max-E-Therm	Water pressure switch open (low flow)	1,636
4	ERR AFS	Pentair MasterTemp	Air flow switch failure	1,496
5	ERR HLS	Pentair MasterTemp / Max-E-Therm	High limit switch tripped (overheating)	1,396
6	ERR IGN	Pentair MasterTemp / Max-E-Therm	Ignition failure after 3 attempts	1,205
7	IF	Hayward Universal H-Series	Ignition failure	944
8	FLO / PS	Hayward HeatPro	No water flow detected	828
9	E01 / E05 / E06	Pentair MasterTemp	Temperature sensor failures (open or shorted)	751
10	LP	Hayward HeatPro	Low refrigerant pressure	596
11	Code 126	Pentair MasterTemp	Shorted water temperature sensor	518
12	No Power	Hayward HeatPro	Blank display, no power to unit	446
13	High Refrig	Pentair UltraTemp	High refrigerant pressure	745
14	HI / HP	Hayward HeatPro	High refrigerant pressure	81
15	PO / OP	Hayward HeatPro	Protection mode activated	84

The top six codes are all Pentair gas heater errors. That is not because Pentair heaters fail more often. It reflects the sheer installed base of MasterTemp and Max-E-Therm units in the field, combined with the complexity of gas combustion systems.

The Big Three: SFS, AGS, and PS

Three error codes together account for nearly half of all heater error searches. Understanding why helps explain what techs deal with most.

ERR SFS: Stack Flue Sensor (2,319 searches)

The most searched heater error code in 2026. ERR SFS means the exhaust temperature is too high. Common causes include a dirty or scaled heat exchanger, blocked exhaust vent, or a failed stack flue sensor. This error is especially common on units over 3 years old that have not had a regular descale.

Full diagnostic guide: Pentair MasterTemp ERR SFS | Max-E-Therm ERR SFS

ERR AGS: Automatic Gas Shutoff (1,883 searches)

The second most searched code. ERR AGS triggers when the heater detects an unsafe gas condition and shuts down. Dirty flame sensors, gas supply issues, and improper venting are the usual suspects. This code often appears alongside ERR SFS because both relate to combustion problems.

Full diagnostic guide: Pentair MasterTemp ERR AGS | Max-E-Therm ERR AGS

ERR PS: Water Pressure Switch (1,636 searches)

Third place goes to a flow problem, not a combustion problem. ERR PS means the heater is not sensing enough water flow to fire safely. Dirty filters, closed valves, and failing pumps are the top causes. This is the error most likely to be caused by something other than the heater itself.

Full diagnostic guide: Pentair MasterTemp ERR PS | Max-E-Therm ERR PS

Pentair vs Hayward vs Jandy: Brand Search Share

Pentair heaters generate 76% of all error code searches. Hayward accounts for 20%, and Jandy rounds out the remaining 4%.

A few things to keep in mind when reading this. Pentair's dominance in search data does not mean their heaters are less reliable. The MasterTemp is the best-selling pool heater in the United States, so more units in the field means more error code searches. Pentair also displays specific alphanumeric error codes on the heater display, which makes them easy to Google. Hayward and Jandy heaters often show less specific indicators, so their techs may search differently.

Pentair Heater Errors: The Full Breakdown

Within Pentair, the MasterTemp and Max-E-Therm share the same control board and error code system. Here is how each code ranks.

The pattern is clear: combustion and exhaust errors (SFS, AGS, AFS, IGN) dominate. These codes all point to the gas burning side of the heater. Flow and sensor errors (PS, HLS, E-codes, 126) are less searched but still represent real field problems.

For the full troubleshooting guide for every Pentair heater code, see our Pentair Heater Error Codes reference or use the interactive MasterTemp Troubleshooter and Max-E-Therm Troubleshooter.

Hayward Heater Errors

Hayward's heater lineup splits between gas (H-Series Universal) and heat pump (HeatPro). The search patterns are different for each.

The H-Series IF (ignition failure) code is the single most searched Hayward heater error. On the heat pump side, flow and refrigerant pressure codes lead. For the full list, see our Hayward Heater Error Codes reference, the H-Series Troubleshooter, or the HeatPro Troubleshooter.

Gas Heaters vs Heat Pumps: Error Profile

One of the clearest findings in this data: gas heaters generate roughly five times more error code searches than heat pumps.

Gas heaters (Pentair MasterTemp, Max-E-Therm, Hayward H-Series, Jandy JXi/LXi) account for about 82% of heater error searches. Heat pumps (Hayward HeatPro, Pentair UltraTemp) make up the remaining 18%.

This gap makes sense. Gas heaters have more moving parts in the combustion process: igniters, flame sensors, gas valves, air flow switches, stack flue sensors, and exhaust systems. Each component can fail independently and throw its own error code. Heat pumps are simpler mechanically but have their own failure modes around refrigerant pressure and defrost cycles.

With the 2026 equipment price increases pushing heater replacement costs higher, techs are more motivated than ever to diagnose and repair rather than replace.

What the Error Types Tell Us

Grouping the top 15 error codes by failure category reveals what actually goes wrong most often.

Nearly half of all heater error searches relate to combustion and exhaust problems. This tells us that heat exchanger maintenance (descaling, cleaning) and gas system inspection are the highest-value preventive services a pool company can offer.

Flow errors (ERR PS, FLO/PS) are the second most searched category, and they are the most likely to be misdiagnosed. When a heater throws a flow error, the problem is usually upstream: a dirty filter, a pump running too slow, or a closed valve. Training techs to check the full hydraulic system before touching the heater saves callbacks.

Surprising Findings

A few patterns in this data were not what we expected.

Gas heaters fail in more ways than heat pumps

Gas heaters produce 5x more error code searches than heat pumps. But it is not just volume. Gas heaters generate errors across six distinct failure categories: combustion, exhaust, flow, ignition, sensors, and wiring. Heat pumps concentrate almost all their failures into two categories: refrigerant pressure and flow. A gas heater tech needs to understand the full combustion sequence. A heat pump tech mostly needs to understand refrigerant and airflow. These are fundamentally different skill sets, and most pool companies treat them as the same job.

1 in 5 heater "failures" are actually plumbing problems

ERR PS and Hayward FLO/PS together account for 18% of all heater error searches. Both codes mean the same thing: not enough water flowing through the heater. In the vast majority of cases, the heater is working correctly. It is doing exactly what it should: refusing to fire without adequate flow. The actual problem is a clogged filter, a VS pump running at too low a speed, or a closed valve somewhere in the plumbing. This means nearly one in five heater service calls could be resolved without ever opening the heater cabinet.

Pentair heaters dominate complaints, but not because they break more

Pentair accounts for 76% of heater error searches. That number looks alarming until you consider that the Pentair MasterTemp is the best-selling residential pool heater in the US and has been for over a decade. More units in the field means more searches. There is also a design factor: Pentair heaters display specific alphanumeric codes (ERR SFS, ERR AGS) on the front panel. Hayward's H-Series just shows "IF" for any ignition problem. Specific codes are easier to search for, which inflates Pentair's share of the data. If Hayward displayed more granular codes, the brand split would likely be closer to 60/40.

Heat exchanger maintenance could prevent the #1 and #2 errors

ERR SFS (high exhaust temperature) and ERR AGS (automatic gas shutoff) are the two most searched codes, and both are commonly caused by the same root problem: a scaled or dirty heat exchanger. When calcium builds up inside the heat exchanger, it insulates the copper tubes and forces exhaust temperatures higher. A $150 descale service once a year could prevent the two most common heater failures in the industry. Most pool service companies do not offer this as a scheduled service.

What This Means for Pool Service Companies

This data has practical implications for how pool service businesses train techs, stock parts, and price repairs.

Parts to Stock

Based on the error frequency data, the highest-turnover heater parts are:

• Stack flue sensors (Pentair 42001-0061S for MasterTemp/Max-E-Therm)
• Flame sensors / igniter assemblies
• Water pressure switches
• Air flow switches (MasterTemp specific)
• High limit switches
• Thermistors and water temperature sensors

Keeping these on the truck means fewer return trips. A stack flue sensor costs about $25 wholesale but saves a $75+ second trip charge.

Training Priorities

If you are onboarding a new tech, start with combustion system basics. The top four Pentair error codes (SFS, AGS, AFS, IGN) all relate to the gas burning system. A tech who understands how the ignition sequence works can diagnose 60% of heater callbacks without a manual.

Second priority: teach them to check flow before opening the heater. ERR PS and Hayward FLO/PS errors account for nearly one in five heater searches, and most are caused by something other than the heater.

Pricing Heater Repairs

The most common heater errors are also the most straightforward to fix. A stack flue sensor swap, flame sensor cleaning, or pressure switch replacement takes 15 to 30 minutes for a trained tech. These repairs should be priced as standard service calls with a parts markup, not as major equipment repairs.

The exception is refrigerant-related heat pump errors (LP, High Refrig). These often require EPA-certified HVAC work and should be priced or subcontracted accordingly.

Methodology