Hayward H-Series FD Heater Thermistor | FDXLTER1931
Hayward Products
SKU: FDXLTER1931
Hayward FDXLTER1931 Thermistor (Water Temperature Sensor) for Universal H-Series FD Heaters
The Hayward FDXLTER1931 is a genuine OEM thermistor (water temperature sensor) used on Hayward Universal H-Series Low NOx “FD” pool heaters. It measures water temperature and sends a signal to the heater control board so the heater can regulate firing accurately and display correct temperature readings.
Fits / Compatibility
- Hayward Universal H-Series FD heaters including: H150FDN, H150FDP, H200FDN, H200FDP, H250FDN, H250FDP, H300FDN, H300FDP, H350FDN, H350FDP, H400FDN, H400FDP
- Also commonly referenced for Universal HC / HDF heater configurations (verify your exact model and parts diagram)
Common Symptoms of a Bad Thermistor
- Displayed water temperature is inaccurate or jumps around
- Heater short-cycles or won’t maintain set temperature
- Temperature-related fault codes or intermittent shutdowns (after confirming proper flow)
- Corroded sensor body or damaged wiring/connector
Key Features
- OEM Hayward replacement for correct signal compatibility and fit
- Restores accurate water temperature sensing for stable heater operation
- Designed for in-ground pool heater applications
Specs (Quick Reference)
- Part Number: FDXLTER1931
- Part Type: Heater Parts (Thermistor / Temperature Sensor)
- Pool Type: In-Ground
- Replacement Part Warranty: 1-Year (Parts Only)
Installation Notes
- Turn off power to the heater at the breaker before servicing.
- Inspect the connector and wiring harness for corrosion or loose pins before installing the new sensor.
- If the heater still shows temperature issues after replacement, inspect water flow, bypass settings, and the control board input.
- Installation should be performed by a qualified technician.
Related Products
- Hayward FDXLTER1931 Thermistor (search)
- Hayward FDXLWPS1930 Water Pressure Switch (FD Heaters) (search)
- Hayward Universal H-Series FD Heater Parts (search)
- Hayward FD Heater Igniters (search)
- Hayward FD Heater Flame Sensors (search)
Maintenance Tips
- Keep the filter clean and valves fully open—flow issues can cause erratic heater behavior that looks like a sensor problem.
- Maintain balanced water chemistry to reduce scale inside the heater, which can affect temperature control and efficiency.
- Inspect heater wiring connections seasonally for corrosion or loose terminals, especially in humid or coastal environments.
Questions about returns? View our return policy.
Hours Of Operation:
Monday - Friday: 7:00 am to 5:00 pm Phoenix Time
Saturday: 8:00 am to 2:00 pm
Sunday: Closed
- We do not ship on Saturday or Sunday.
- Orders totaling more than $300 will require signature confirmation upon delivery.
- We process and prepare orders for shipment within 1 business day. Please note that many other pool supply retailers require 3–5 days of handling time before shipping.
- Orders placed after 1:00 pm Phoenix Time may not be eligible for same-day shipment.
- Expedited shipping options are available at checkout.
Return Policy:
- Products that are received damaged will receive a refund in store credit.
- Most products are eligible for return within 30 days of receipt, except where noted below.
- To initiate a return, please complete an RMA form prior to sending your item back.
- Original shipping costs are non-refundable and will be deducted from the return credit.
- Items returned missing accessories or original packaging, or that are not in the same condition as received, may be subject to a restocking fee of up to 100% depending on the condition of the item upon return.
- Some returns will be charged an automatic 15% restocking fee.
- We are unable to issue refunds for items that have been damaged or rendered inoperable due to installer error.
- Please complete the return form to receive your RMA number and return shipping label.
- Chemical products are not eligible for return under any circumstances.
- The Pentair Colorsync 618031 is not eligible for return.
- Pool cleaners are not eligible for return.
- Opened seals and o-rings are not eligible for return.
- Capacitors are not eligible for return.
- Plastic popup tools are not eligible for return.
- Automation components and circuit boards are not eligible for return.
- If a light is returned due to a reported malfunction and is found to be fully operational upon testing, return shipping costs and a restocking fee will be deducted from the refund.
- Orders refused at the time of delivery will be subject to the original shipping costs being deducted from the refund.
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