Pentair MasterTemp error codes

A MasterTemp shows a code when it has stopped, or refused to start, because one of its safety checks failed. The code tells you which check failed. It doesn't tell you which part has failed, and those are different questions.

Everything here comes from Pentair's MasterTemp Pool and Spa Heater Installation and User's Guide, P/N 472592 Rev. Q (7/30/23). Page numbers are the printed page numbers in that manual, which covers the MasterTemp 175, 200, 250, 300 and 400 in natural gas and propane, including the HD and ASME versions (p. 1).

If you smell gas, leave the area and call your gas utility from a safe place before anything else. Pentair's instructions say not to light any appliance, not to touch electrical switches, not to use a phone inside the building, and to call the gas supplier from a neighbor's phone. If you can't reach the supplier, call the fire department (p. 42).

The codes at a glance

Code	What the heater is reporting	How it clears (per the manual)	Manual page
ERR PS	Water pressure switch open: not enough water flowing through the heater	Clears itself once flow is established	p. 48 (Table 8); p. 45
ERR HLS	High-limit switch open: water after the first pass through the heat exchanger is above 135°F	Clears itself once the temperature falls below 135°F	p. 48 (Table 8)
ERR AFS	Air flow switch open: the blower isn't running, or air through it is restricted	Resumes if air flow is restored within 60 seconds; otherwise press HEATER OFF	p. 48 (Table 8)
ERR IGN	The ignition control module couldn't light the heater	Press HEATER OFF	p. 48 (Table 8)
ERR AGS	Automatic gas shutoff: water after the second pass through the heat exchanger is above 140°F	Front-panel buttons disabled; reset by cycling power	p. 48 (Table 8)
ERR SFS	Stack flue temperature above 480°F	Front-panel buttons disabled; reset by cycling power	p. 48 (Table 8)
E05	Stack flue sensor open	Follow the SFS chart	p. 48 (Table 8); p. 54
E06	Stack flue sensor shorted	Front-panel buttons disabled; reset by cycling power	p. 48 (Table 8); p. 54
E01	Water temperature sensor open	Press HEATER OFF	p. 48 (Table 8); p. 53
126	Water temperature sensor shorted	Follow the sensor chart	p. 48 (Table 8); p. 53

The most important line in the manual is about the last nine codes. Pentair says not to operate the heater while ERR HLS, ERR AFS, ERR IGN, ERR AGS, ERR SFS, E01, E05, E06 or 126 is displayed. It says to shut the heater down and have a qualified service technician check the system (p. 45). "How it clears" in the table describes how the control behaves. It isn't a suggestion to keep resetting the heater.

ERR PS — not enough water flow

This is the one code you can usually work through yourself, because the cause is usually outside the heater.

The heater has a water pressure switch that closes only when enough water is moving through it. ERR PS means the switch is open, and the heater won't fire until it closes. Once flow is restored, the code clears itself (p. 48).

What you can safely check:

• The pump is running. Pentair's troubleshooting section begins by confirming that the pump is running correctly and the time clock is set and running (p. 48).
• Baskets and filter. Pentair says that if the pump is running, ERR PS usually means the filter and/or skimmers need cleaning, and some filters may need backwashing (p. 45).
• Valve positions. Water has to be routed through the heater. If valves were changed for spa mode or a cleaner, set them back.
• Pump speed. On a variable-speed pump, a low-speed program may not move enough water. Each MasterTemp model has a minimum flow (p. 14, p. 51):

MasterTemp model	Minimum flow	Maximum flow	Manual page
175	20 gpm	120 gpm	p. 14 (Table 1); p. 51
200	20 gpm	120 gpm	p. 14 (Table 1); p. 51
250	25 gpm	120 gpm	p. 14 (Table 1); p. 51
300	30 gpm	120 gpm	p. 14 (Table 1); p. 51
400	40 gpm	120 gpm	p. 14 (Table 1); p. 51

When to stop: Pentair says that if ERR PS stays on after the filter and skimmers have been serviced, the system should be checked by a qualified service technician (p. 45). The manual's chart then moves on to the pressure switch, its wiring and its adjustment, which are inside the heater (p. 51, p. 53).

ERR HLS and ERR AGS — water too hot inside the heater

Both codes mean the water inside the heat exchanger got hotter than it should. ERR HLS trips above 135°F after the first pass, and ERR AGS trips above 140°F after the second (p. 48).

Pentair's diagnostic chart for these two codes starts with checking that the water flow is above the heater's minimum and that the water entering the heater is below 104°F. After that it moves to the internal bypass valve, the thermal governor and possible blockage in the heat exchanger (p. 53). Low flow is the first suspect, so a clean filter and a running pump are worth confirming. But the manual says not to operate the heater while either code is showing (p. 45).

ERR AFS — combustion air problem

The heater uses a blower to move combustion air, and an air flow switch checks that the blower is working. ERR AFS means the switch is open: the blower isn't running, or air through it is restricted (p. 48).

Pentair's chart for ERR AFS looks for blockage in the blower intake, heat exchanger or exhaust, an exhaust run that is too long, and damaged or misrouted tubing to the switch, before looking at the switch and the blower (p. 53). From outside, you can check that nothing is blocking the heater's exhaust or vent openings. The manual's start-up checklist asks owners to keep the area around the heater and its vent clear of debris (p. 42). Everything past that is inside the cabinet.

ERR IGN — the heater didn't light

The ignition control module tried to light the burner and couldn't (p. 48).

Pentair's chart for this code checks gas pressure, the hot surface igniter, the gas valve and the voltages that control them (p. 52). All of that is technician work on a gas appliance. The useful thing you can check is whether gas is reaching the house. If the stove, water heater or other gas appliances are also out, the problem is upstream of the heater. Tell the technician that when you call.

ERR SFS, E05 and E06 — flue temperature

ERR SFS means the flue gas leaving the heater is above 480°F. E05 and E06 mean the sensor that measures it is reading open or shorted (p. 48).

Pentair's chart for ERR SFS covers the fuel supply, the thermal regulator, and the heat exchanger coil (leaks, liming, soot or low flow) (p. 54). Excessive flue temperature is a combustion condition, so leave the heater off until it has been checked.

E01 and 126 — water temperature sensor

The heater reads water temperature through a thermistor. E01 means the sensor circuit reads open, and 126 means it reads shorted (p. 48). The manual's chart checks the thermistor wiring and then the thermistor itself (p. 53). The heater can't control temperature without that reading, so it stays off.

Messages you may see on automation

If your MasterTemp is connected to a Pentair automation system, the ignition module's status can also appear there. The manual lists CONTROL FAULT, AIR FLOW FAULT, FLAME NO CALL FOR HEAT, IGNITION LOCKOUT, WEAK FLAME and GOOD FLAME as messages displayed on the automation system. WEAK FLAME and GOOD FLAME can also be viewed in the heater's own menu (p. 45).

No code, but no heat

If the display shows no error and the heater won't fire:

• Setpoint. It has to be above the actual water temperature, or the burner won't fire (p. 43). The adjustable range is 65°F to 104°F (p. 46).
• POOL MAX and SPA MAX. These menu settings cap the operating temperature for each body of water (p. 47).
• History. The HISTORY menu item scrolls through the last five heater errors (p. 47), which can catch a code that has come and gone.

Safe to check, and where to stop

Safe from outside the heater: the pump, its schedule and speed, the baskets and filter, the valve positions, the setpoint, the menu settings, the error history, whether other gas appliances work, and whether the area around the heater and its vent is clear.

Stop there. Pentair's troubleshooting pages warn against jumpering switch terminals to get around a failed safety switch (p. 49). Its operating instructions say that if the gas control can't be turned by hand, don't try to repair it and call a qualified service technician (p. 42).

Getting it diagnosed

Mobile Pool Repair's heater diagnostic reads the code against Pentair's documentation, measures the flow through the heater, checks the pump speed and schedule behind that flow, and checks the filter and valve positions on the pad. Pentair's own charts for ERR PS, ERR HLS and ERR AGS start with flow, so that is where the visit starts. You get a clear answer on what has failed and what fixing it involves.

A diagnostic is $120, and the $120 is credited toward your repair if you go ahead. Start from the pool heater diagnostic page, or see the broader guide to a pool heater not heating.

Sources

• Pentair, MasterTemp Pool and Spa Heater Installation and User's Guide, P/N 472592 Rev. Q (7/30/23). Error and fault codes: Table 8, p. 48. Page numbers above are the printed page numbers.

Pentair and MasterTemp are trademarks of Pentair. They are named here only to identify the equipment.