We Found a Gas Leak and a Mouse Nest in the Same Month — Both in Pool Heaters

We found a gas leak in a pool heater last month that the homeowner had no idea about. The heater had not been used since spring. There was no smell because the leak was small — just enough gas escaping from a corroded fitting to be dangerous but not enough to detect by nose from the back door. We found it because we check heater connections at every visit, not just when the homeowner asks us to turn it on.

A different pool, different week — we opened a heater access panel for a routine inspection and found a mouse nest built inside the combustion chamber. The mice had chewed through the igniter wiring and packed nesting material around the burner orifices. If the homeowner had fired that heater without inspection, the nest material would have ignited inside the combustion chamber — creating a fire risk inside a device connected to a natural gas line.

These are the things homeowners do not know about because they never open the heater panel. Here is what we find, how often we find it, and why equipment inspection is the most important part of pool service that most companies skip entirely.

The Gas Leak

How It Happens

Pool heaters connect to your home's natural gas line through a series of fittings — typically black iron pipe or corrugated stainless steel tubing (CSST) with brass connections. These connections are exposed to the elements on your equipment pad — rain, humidity, temperature cycling from 30°F winter nights to 110°F summer afternoons, and chemical fumes from the pool water.

Over years, connections can develop micro-leaks from:

Thermal expansion and contraction. Metal fittings expand in heat and contract in cold. After thousands of cycles, thread joints can develop microscopic gaps that allow gas to seep through.

Corrosion. Chemical fumes from pool water — chlorine gas, acidic vapors from muriatic acid — accelerate corrosion on metal fittings. Brass connections develop green patina, black iron pipe rusts at the threads.

Vibration. The heater's internal components — igniter, blower motor, gas valve — create low-level vibration during operation. Over years, vibration can loosen threaded connections incrementally.

Why the Homeowner Did Not Know

Small gas leaks do not smell from 20 feet away. The mercaptan odorant added to natural gas (the "rotten egg" smell) is detectable by nose at certain concentrations — but a micro-leak on an outdoor equipment pad disperses quickly in open air. The homeowner walking past the equipment pad would not smell it. Someone standing directly next to the heater with their nose near the fitting might detect a faint odor — but nobody does that.

How We Found It

We apply a soapy water solution (or commercial leak detection fluid) to every gas connection during our quarterly heater inspection. Bubbles forming at a connection indicate a gas leak — even leaks too small to smell. The test takes 5 minutes and catches leaks that would otherwise go undetected until they become dangerous.

The Fix

Tighten the fitting. If the leak is at a threaded connection that has loosened, tightening with pipe dope or Teflon tape and a wrench resolves it. Cost: $0 in parts, included in our service visit.

Replace the fitting. If the fitting is corroded through, it needs replacement. A new brass fitting or gas-rated coupling costs $5-20 in parts. Labor: $50-100.

Call the gas company for major issues. If the leak is on the supply side (before the heater's gas valve) or involves the gas line itself rather than a fitting, we shut the heater off, close the gas valve, and recommend the homeowner contact their gas utility or a licensed plumber for the supply line repair.

What could have happened: A gas leak near an ignition source — the heater's own burner, a nearby electrical connection, or even a spark from the pump motor — creates a fire or explosion risk. Small leaks build up gas in enclosed or semi-enclosed spaces (like a heater cabinet or a covered equipment pad area). One ignition event and the accumulated gas ignites.

The Mouse Nest

Why Mice Love Pool Heaters

A pool heater that sits unused for 5-7 months (April through October in Frisco — when nobody needs heat) is a perfect mouse habitat:

Warm and sheltered. The heater cabinet is enclosed, protected from rain and wind, and retains warmth from residual pilot heat or solar absorption.

Dark and undisturbed. Nobody opens the heater panel from April to October. Mice have months of uninterrupted nesting time.

Access points everywhere. Heater cabinets have ventilation openings for combustion air intake and exhaust. These openings are large enough for mice (and rats, and squirrels) to enter.

What We Found

The mouse nest was built directly inside the combustion chamber, on top of and around the burner tubes. The nesting material — shredded insulation, leaves, grass, dryer sheet fragments (mice love these) — was packed between and around the gas orifices. The igniter wire had been chewed through — mice chew wiring for the copper and for nesting material.

What Would Have Happened

If the homeowner turned the heater on without inspection:

Scenario 1 (most likely): The chewed igniter wire prevents ignition. The heater clicks repeatedly, fails to light, and displays an ignition failure code. Gas flows into the combustion chamber but does not ignite. The heater eventually locks out on safety. Unburned gas vents through the exhaust — a smell issue but not immediately dangerous.

Scenario 2 (dangerous): The igniter wire is partially chewed but still functional. The igniter sparks. The nest material in the combustion chamber ignites — a burst of flame inside the heater cabinet fed by nesting material and accelerated by the gas flow. Fire inside an enclosed cabinet connected to a gas line.

Scenario 3 (also dangerous): The gas flows, fails to ignite on the first attempt, fills the combustion chamber with gas, and then ignites on a delayed spark. The accumulated gas creates a small explosion inside the heater — blowing the access panel open and potentially cracking the heat exchanger.

The Fix

Remove the nest material completely. Inspect all wiring for chew damage — replace any damaged wires. Clean the burner orifices of debris. Test the igniter and flame sensor. Verify proper gas flow and ignition.

Cost: $75-150 for cleaning and wire repair. Versus the potential cost of a fire, a destroyed heater ($2,500-4,000), or worse.

Prevention

Inspect the heater in September before the first use of the season. Open the access panel, look inside the combustion chamber, check for nests and wiring damage.

Install pest screens on the heater's ventilation openings. Fine mesh screens ($5-10) block mice and insects from entering while still allowing combustion air flow. Not all heater models accommodate screens easily — check with your technician.

Run the heater briefly once per month during off-season. A 10-minute run cycle every 4-6 weeks during summer discourages nesting (the heat and noise deter mice) and keeps the ignition system exercised.

Why Equipment Inspection Matters More Than Chemistry

Any pool technician can test chlorine and add chemicals. That is the baseline of pool service. The difference between a cleaning service and a real service company is equipment inspection — the part you cannot see from the back door.

What we check at every visit that most services skip:

• Pump for unusual noise, vibration, leaks, air in the housing
• Filter pressure trend (rising pressure = loading filter)
• Heater connections and combustion chamber (quarterly deep inspection)
• Salt cell plates for scaling (monthly visual)
• Electrical connections for corrosion or heat damage
• Plumbing unions and fittings for leaks
• Timer and automation operation

The gas leak and the mouse nest were found during routine inspections — not emergency calls. The homeowner did not know about either problem. If we had been a cleaning-only service that tests chlorine and leaves, both would have gone undetected until something failed — or something caught fire.

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