Pool Heater Not Working in McKinney, TX — Common Causes and Fixes

The first warm weekend of spring in McKinney and you flip the heater switch expecting 85-degree water by Saturday afternoon. Nothing happens. Or worse — it fires up, runs for two minutes, then shuts off. Or it runs continuously and the temperature doesn't budge. Each of these failure modes points to a different cause, and knowing which one you're dealing with saves you time, money, and the frustration of replacing parts that weren't the problem.

McKinney's pool inventory spans everything from brand-new builds in Craig Ranch's latest phases to 15+ year old pools in Stonebridge Ranch and the neighborhoods around Eldorado Parkway. The heater problems in newer pools tend to be installation or settings issues. The problems in older pools tend to be wear, scale, and component failure. Here's the diagnostic rundown, ordered by how frequently we encounter each cause in McKinney service calls.

Cause 1: Low Water Flow (Most Common)

Pool heaters have a flow switch or pressure switch that prevents the heater from firing if water flow is insufficient. This is a safety feature — heating without adequate water flow can damage the heat exchanger and create a fire risk in gas heaters.

If the heater turns on, fires briefly, and then shuts off — or displays a "LO" or "FLO" error code — insufficient water flow is the most likely cause.

Common flow-related issues:

• Dirty filter. A clogged filter restricts flow through the entire system. Clean or backwash the filter and test the heater again. This solves the problem about 40% of the time.
• Closed or partially closed valves. Check every valve between the pump and the heater. A valve accidentally turned to the wrong position — especially on pool/spa combo plumbing in McKinney homes with both — restricts flow enough to trip the switch.
• Pump not running at adequate speed. If you have a variable speed pump programmed to run at low speed, the flow rate may be below the heater's minimum requirement. Most heaters need 20-40 GPM minimum. A VSP running at 1,200 RPM may not produce enough flow. Program the pump to boost speed when the heater is running.
• Clogged pump impeller. Debris wrapped around the impeller reduces output. Turn off the pump, open the strainer basket, and check for debris in the impeller housing.

Cause 2: Dirty or Failed Ignition Components (Gas Heaters)

Gas pool heaters (natural gas or propane) use either a standing pilot light or an electronic ignition (hot surface igniter or spark igniter) to light the burner. If the ignition system can't light the gas, the heater goes through its ignition sequence, fails, and locks out.

Standing pilot heaters (older units): The pilot light may have blown out — relight it per the manufacturer's instructions on the heater label. If the pilot won't stay lit, the thermocouple is likely failed. Thermocouples are inexpensive parts ($15-30) but require specific knowledge to replace safely.

Electronic ignition heaters (newer units): The hot surface igniter (a glowing element that lights the gas) degrades over time and eventually can't reach ignition temperature. Replacement igniters cost $30-80 depending on the brand. A dirty or corroded flame sensor can also prevent the heater from recognizing that the burner has lit — the system shuts off the gas as a safety measure even though combustion is occurring.

For McKinney specifically: Spider webs and insect nests in the burner tray are a surprisingly common cause of heater failure. Mud dauber wasps build nests inside heater cabinets during the off-season, blocking burner orifices and gas passages. If your heater hasn't been used since fall, inspect the burner tray and gas orifices for obstructions before troubleshooting electrical components.

Cause 3: Tripped High-Limit Switch

Every pool heater has a high-limit switch (also called a thermal fuse or temperature limit) that shuts the heater down if the heat exchanger temperature exceeds a safe threshold — typically 135-150°F. This prevents overheating that could damage the exchanger or create a burn hazard.

The high-limit trips when:

• Scale buildup on the heat exchanger insulates the surface, causing localized overheating. This is common in McKinney pools with hard municipal water — calcium scale accumulates inside the exchanger over years of use.
• Low water flow doesn't carry heat away fast enough (see Cause 1).
• Thermostat malfunction keeps the burner firing after the target temperature is reached.

Most heaters have a manual reset button for the high-limit switch — usually a small red button inside the heater cabinet. Press it to reset. If the heater fires normally and doesn't trip again, it was a one-time event. If it trips repeatedly, there's an underlying issue (usually scale or flow) that needs addressing.

Cause 4: Scaled Heat Exchanger

This is the chronic version of Cause 3. Over years of operation in McKinney's hard water, calcium carbonate deposits build up inside the heat exchanger's narrow passages. The scale reduces heat transfer efficiency (the heater runs but water doesn't get warm) and restricts flow (triggering the flow switch or high-limit).

Symptoms of a scaled exchanger:

• Heater runs normally but water temperature barely increases
• Heater cycles on and off repeatedly (short cycling)
• High-limit trips frequently
• Heating takes twice as long as it used to

The fix: A professional descaling — flushing the heat exchanger with a vinegar or muriatic acid solution — can restore a moderately scaled exchanger. For heaters in Stonebridge Ranch or the older Craig Ranch sections that have never been descaled, the improvement can be dramatic.

If the scale is severe — years of accumulation with no maintenance — the exchanger may be damaged beyond cleaning. Exchanger replacement costs $800-1,500 for parts and labor, which often approaches the cost of a new heater. At that point, replacement usually makes more sense than repair.

Cause 5: Gas Supply Issues

If the heater doesn't fire at all — no ignition attempt, no clicking, no gas smell — the gas supply may be interrupted.

Check the gas valve. There's a manual shut-off valve on the gas line leading to the heater. Make sure it's in the open position (handle parallel to the pipe).

Check other gas appliances. If your gas stove and water heater are also off, the issue is with your main gas supply — contact your gas utility.

Low gas pressure can prevent the heater from firing even when gas is available. This is more common in McKinney homes at the end of a long gas main run, or in newer developments where the gas infrastructure is still being built out. A gas pressure test (done by a licensed plumber or HVAC tech) can identify whether your heater is receiving adequate pressure.

LP (propane) heaters: Check the propane tank level. A tank that reads 10-15% may not deliver adequate pressure to fire the heater, even though there's still propane in the tank. The regulator can also freeze in cold weather — pouring warm (not hot) water over the regulator can free it.

Cause 6: Electrical and Control Issues

Tripped breaker. Pool heaters draw significant current on startup. Check the breaker panel — the heater should have a dedicated breaker. Reset it if tripped. If it trips again immediately, there's a short or ground fault in the heater's electrical components — stop and call a technician.

Corroded wiring. Outdoor equipment in McKinney's climate deals with heat, humidity, and temperature swings that corrode electrical connections over time. Inspect the wiring connections inside the heater cabinet for green corrosion, loose terminals, or heat-damaged insulation.

Control board failure. Modern pool heaters have electronic control boards that manage ignition sequencing, temperature control, and error diagnostics. These boards can fail from power surges (common during North Texas thunderstorms), moisture intrusion, or age. Replacement boards cost $300-600 depending on the heater brand and model.

A whole-house surge protector ($200-400 installed) protects the heater's control board — along with every other electronic device in your home — from lightning-induced surges. For McKinney homeowners who've replaced a control board once, the surge protector prevents it from happening again.

Cause 7: Heat Pump Specific Issues

If you have a heat pump (electric) rather than a gas heater, additional failure modes include:

Low ambient temperature. Heat pumps extract heat from the surrounding air. When air temperature drops below 50°F, most heat pumps lose efficiency dramatically and may not heat effectively. This is why heat pumps in McKinney work well from April through November but struggle in December through February.

Dirty evaporator coil. The outdoor coil (looks like an AC condenser) needs airflow to transfer heat. Leaves, debris, and pollen blocking the coil reduce efficiency. Rinse the coil with a garden hose seasonally.

Refrigerant leak. If the heat pump runs but produces cool or lukewarm air from the fan, a refrigerant leak is likely. This requires a licensed HVAC technician to diagnose and repair — not a pool technician.

When to DIY and When to Call a Pro

Safe for homeowners to check:

• Filter cleanliness (clean it)
• Valve positions (open them)
• Gas valve position (open it)
• Breaker status (reset it)
• Pilot light (relight it per instructions)
• Pump speed settings (increase flow)
• High-limit reset button (press it once)

Call a professional for:

• Anything involving gas line connections or gas pressure
• Control board replacement
• Heat exchanger descaling or replacement
• Igniter or flame sensor replacement
• Any issue that recurs after you've reset it once
• Any situation where you smell gas strongly — leave the area and call your gas utility

Pool heaters involve gas, electricity, and water in close proximity. The DIY checklist above is safe and covers the most common issues. Anything beyond that should be handled by someone trained in pool heater service.

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