The Pentair MasterTemp 250 is a popular natural gas or propane pool heater known for its compact design, fast heating, and efficiency. When it’s running properly, you can raise your pool temperature quickly and extend your swim season with ease. But like any gas-fired pool heater, the MasterTemp 250 can run into issues over time. Understanding the warning signs and knowing how to troubleshoot can save you from unnecessary downtime.
This guide covers the most common MasterTemp 250 problems, their likely causes, and practical steps you can take before calling in a technician. We’ll also share maintenance tips to help you keep your heater running for years.
How the MasterTemp 250 Works
The MasterTemp 250 heats pool water by circulating it through a copper heat exchanger while burning natural gas or propane in a combustion chamber. The control system monitors water temperature, flow rate, and safety sensors to ensure safe operation. If something isn’t right, the system shuts down and may display an error code on the digital control panel.
Common MasterTemp 250 Problems and Fixes
1. Heater Won’t Turn On
Symptoms: Control panel is blank, or no lights come on when pressing the power button.
Possible causes:
- Tripped breaker or GFCI outlet
- Loose or damaged wiring connection
- Defective power switch
- Faulty control board
What to do:
- Check your pool equipment breaker panel and reset if tripped.
- Inspect GFCI outlets and reset if necessary.
- Verify all wiring connections are secure and free of corrosion.
- If power is reaching the unit but nothing lights up, the power switch or control board may need replacement.
2. Heater Won’t Ignite
Symptoms: Display turns on, blower fan may run, but no flame is produced.
Possible causes:
- Gas supply valve closed
- Low gas pressure
- Faulty igniter
- Dirty or blocked burners
- Defective flame sensor
What to do:
- Ensure gas supply valve is fully open.
- Check propane tank level or natural gas supply line pressure.
- Inspect igniter for cracks or wear; replace if damaged.
- Clean burner tray to remove debris and spider webs.
- Clean flame sensor with fine steel wool to restore proper detection.
3. Heater Starts, Then Shuts Off
Symptoms: Unit fires, runs for a short period, then shuts down before reaching set temperature.
Possible causes:
- Low water flow triggering pressure switch
- Overheating triggering high-limit switches
- Flame loss during operation
What to do:
- Clean or backwash pool filter to improve flow.
- Ensure pool pump is running at adequate speed.
- Inspect high-limit switches for proper operation; replace if defective.
- Check for venting issues or downdrafts affecting flame stability.
4. Slow Heating or Not Reaching Temperature
Symptoms: Heater runs but pool takes too long to heat.
Possible causes:
- Scale buildup in heat exchanger reducing efficiency
- Low gas pressure affecting flame size
- Thermostat set too low or out of calibration
- Cold weather heat loss from pool
What to do:
- Check thermostat settings and increase if needed.
- Inspect heat exchanger for scale; descale if necessary.
- Have a technician measure and adjust gas pressure.
- Use a pool cover to reduce heat loss overnight.
5. Error Codes on Display
The MasterTemp 250 displays error codes to help pinpoint problems:
- AGS – Auto Gas Shutoff: Overheating or improper combustion.
- HLS – High Limit Switch open: Over-temperature condition.
- PS – Pressure Switch open: Low water flow.
- SFS – Stack Flue Sensor fault: Excessive exhaust temperature or sensor failure.
- ROL – Flame rollout switch open: Possible blocked burners or flue gases spilling out.
What to do: Address the cause of the error before resetting the unit. Repeated tripping of safety devices indicates a real hazard that must be corrected.
6. Unusual Noises
Symptoms: Whistling, popping, or banging noises during operation.
Possible causes:
- Scale inside heat exchanger causing water to flash boil
- Dirty burners causing uneven flame
- Air in gas line
What to do:
- Flush or descale heat exchanger.
- Clean burners thoroughly.
- Have a qualified technician purge air from the gas line.
7. Soot or Black Marks on Heater
Symptoms: Dark soot deposits around exhaust or on heater surfaces.
Possible causes:
- Incomplete combustion from dirty burners
- Blocked or restricted venting
- Improper gas-to-air ratio
What to do:
- Shut off heater immediately.
- Inspect and clean burners.
- Clear vent obstructions.
- Have gas mixture adjusted by a professional.
Maintenance Tips to Prevent Problems
- Keep pool water balanced to prevent scaling or corrosion in the heat exchanger.
- Inspect and clean filter regularly for proper water flow.
- Check for debris or obstructions in heater vent and combustion air inlets.
- Have gas pressure checked annually by a qualified technician.
- Schedule a professional inspection before each swim season.
When to Call a Professional
Some repairs require specialized tools and expertise, especially those involving gas and combustion. Call for service if:
- You smell gas near the heater
- Error codes persist after basic fixes
- There’s water leaking inside the heater cabinet
- You see burn marks, melted wiring, or severe corrosion
Quick Recap
- No power: Check breaker, GFCI, wiring, switch, and control board.
- No ignition: Confirm gas supply, clean igniter, check burners and flame sensor.
- Short cycling: Check water flow, high-limit switches, and venting.
- Slow heating: Descale heat exchanger, verify gas pressure, cover pool.
- Error codes: Address root cause, don’t just reset.
- Noises or soot: Clean burners, check venting, adjust combustion.
The MasterTemp 250 is a dependable and efficient pool heater when maintained correctly. By learning the common symptoms and knowing what to check first, you can often get your heater running again without a costly service call—and keep your pool warm all season long.