Every year it's the same week. The first real cold front pushes through, thousands of Houston pool owners reach for the heater at once, and a large share of them get nothing. It isn't coincidence, and it usually isn't the cold — it's what happened during the five months nobody touched it.
Redzone Pools repairs pool and spa heaters across Cypress, Tomball, Katy, Spring and Greater Houston — licensed, insured, usually same day.
In colder states a pool heater works through autumn and gets shut down for winter. Here it's inverted. Nobody in Houston heats a pool in July — the water sits in the high eighties on its own. So the heater goes untouched from roughly April through September, five months of standing idle in a warm, humid, mostly-outdoor cabinet.
Then one night in late October or early November the temperature finally drops, and every heater in the county is asked to light on the same evening. That's our single busiest call week of the year, and the failures are remarkably consistent.
The important thing to understand: the heater didn't break in the cold. It broke — or was colonised — sometime over the summer, and nobody knew, because nobody asked it to do anything.
A warm, sheltered, undisturbed metal box in a Gulf Coast summer is attractive real estate. Here is what we actually find when we open one up in November.
The classic. They pack mud nests into the burner tray and the venturi — exactly the passages that have to stay clear for air and gas to mix properly. A single nest is enough to stop ignition.
Fire ants in particular will colonise a control board. They bridge contacts, corrode terminals, and produce faults that look electrical because they are — just not the kind anyone expects.
Nesting material in the flue restricts exhaust. The heater either won't stay lit or trips a safety, because the combustion air path is no longer what it was designed around.
Five months of Gulf Coast humidity works on burner trays, flame sensors and connections. Nothing dramatic — just enough oxidation to stop a sensor reading a flame it's actually looking at.
None of these are exotic. They're what happens to any gas appliance left idle outdoors in this climate for most of a year, and they're why "it worked fine in March" tells you almost nothing about whether it'll light in November.
This is the one that costs people money, and it's worth understanding before you buy a part.
A gas heater doesn't just light the burner — it has to confirm the flame is actually there, using a flame sensor. If the sensor can't see the flame it's looking straight at, the control shuts the gas off within seconds. From the deck, that looks identical to an igniter that never lit anything: a click, a brief whoosh, then nothing.
Five idle months of humidity is exactly what leaves a light film on a flame sensor. So the heater lights, fails to confirm, and shuts down — and the owner, reasonably, concludes the igniter is dead and buys one.
The new igniter changes nothing, because the igniter was never the problem. Distinguishing the two takes a meter and about two minutes, and it's the first thing worth checking on a heater that tries to light and gives up.
Before assuming the worst, look at the display. Most modern heaters name the fault rather than just refusing to work, and the code narrows things fast.
An ignition fault points at the burner, igniter or flame sensor — the group above. An air flow fault points at something restricting the combustion air path, which is exactly what a nest in the venturi or vent produces. A pressure or flow fault is usually not the heater at all, but circulation — often a filter that needs cleaning after a long season.
On a Pentair MasterTemp or Max-E-Therm, every code and what it means is set out in our MasterTemp error code guide. If the heater fires but the water never warms, that's a different path entirely — see a heater that runs but won't heat.
Write the code down before cycling power. Several clear themselves on restart, and a code you've lost is diagnosis time you end up paying for.
This is the single most useful thing in this article, and it takes ten minutes.
Some time in early October — while it's still warm and nothing is urgent — turn the heater on and let it run for fifteen or twenty minutes. Watch that it lights, stays lit, and actually warms the water.
If it fails, you've found out on a mild afternoon when technicians are available and parts can be ordered without drama. If it works, you've confirmed it and you can forget about it.
Compare that with the alternative: discovering the problem at six in the morning on the coldest day so far, in the same week every other pool owner in the county is discovering theirs. That's the week when nobody can get to you for days, and it's entirely avoidable.
While the cover is off, a quick look for mud nests around the burner tray and any obstruction at the vent is worth the two minutes it takes — you can spot most of this without tools.
One more thing worth knowing: our hard fill water quietly narrows heat exchanger passages over the years, which is a slower but equally real reason an older heater struggles. That mechanism is covered in why Houston's fill water is hard on pool heaters.
Reasonable to do yourself: note the error code, check the gas supply valve is open, confirm the pump is running and the filter is clean, make sure the thermostat is set above current water temperature and in the right mode, look for obvious nests or debris around the cabinet and vent, and run the October test.
Stop and call: anything inside the gas train, anything requiring the burner tray to come out, any code that returns straight after a reset, and any smell of gas. This is a gas appliance with safety interlocks that exist for good reason — clearing a nest out of a burner tray properly means knowing what you're looking at when it's back together.
That's our day job. See pool heater repair, or just tell us the code and we'll usually know what we're walking into.
Usually because it has been idle since spring. In Houston nobody heats a pool between roughly April and September, so the heater sits untouched for five months in a warm, humid outdoor cabinet. In that time mud daubers and wasps build nests in the burner tray and venturi, ants and roaches get into control boards, rodents nest in the vent, and humidity leaves a film on the flame sensor. The cold night didn't break it — it just asked it to work for the first time since the problem developed.
Very often a dirty flame sensor rather than a failed igniter. The heater has to confirm the flame is present, and if the sensor can't detect it, the control shuts the gas off within seconds as a safety measure. From the deck this looks identical to an igniter that never lit. Replacing the igniter changes nothing, because the igniter was doing its job. A technician can distinguish the two in a couple of minutes with a meter — worth checking before buying any part.
Yes, and it's one of the most common things we find. Mud daubers pack solid nests into the burner tray and venturi — the passages that have to stay clear for gas and air to mix correctly. A single nest can prevent ignition outright or cause the heater to fail a safety check. A warm, sheltered, undisturbed metal cabinet through a Gulf Coast summer is close to ideal nesting conditions, which is why this is a seasonal pattern here rather than a freak occurrence.
Early October. Run it for fifteen or twenty minutes and confirm it lights, stays lit and actually warms the water. If something is wrong you'll find out on a mild afternoon when technicians are available and parts can be ordered calmly — rather than at 6am on the coldest morning of the year, in the same week every other pool owner in the county has the same problem and nobody can reach you for days.
Be careful here. A heater needs its air path clear, and a cover that traps moisture or blocks ventilation can create as many problems as it prevents. Never seal a gas appliance's combustion air or vent openings. If you want to reduce pest access, the practical approach is to keep the cabinet closed and the vent screen intact, and to inspect before the first use of the season rather than relying on a cover to keep things out.
Partly. Checking the gas valve is open, confirming the pump runs and the filter is clean, setting the thermostat above current water temperature, and looking for obvious nests or vent obstructions are all reasonable. Anything inside the gas train, anything requiring the burner tray to be removed, and any code that returns immediately after a reset needs a licensed technician. If you smell gas at any point, shut it down and call. The safety interlocks on these units exist because the failure modes are serious.
Book a pre-season heater check while the calendar is still open, or tell us the code it's showing and we'll tell you what you're looking at. Licensed, insured, serving Cypress and Greater Houston.