Why a pool heater is not heating

A pool heater that is not heating usually has a specific fault in the heater itself, and finding that fault comes before replacing parts. Sullivan's Pool Service diagnoses and repairs gas and heat-pump pool heaters, and the diagnosis identifies the actual problem rather than swapping parts on a guess. Send the heater's make and model and what it is doing, and you get a quote for your approval before any work starts. Do not open electrical equipment yourself to gather this information.

By Ryan Sullivan · Published September 30, 2026

Drafted with AI assistance from its cited sources and checked automatically before publication: every figure must appear in those sources. How our guidance is prepared.

Heater repair starts with a diagnosis

When a pool heater stops putting out warm water, the temptation is to guess at the culprit and start replacing pieces until something works. We take a different approach. Before any repair happens, we diagnose the actual fault, whether the heater runs on gas or is a heat pump, so the fix matches the problem rather than a hunch about it.

That distinction matters because a heater that fails to heat can have several different causes, and swapping a part that turns out to be fine costs you money without solving anything. Diagnosis first means the repair is aimed at what is genuinely wrong.

The work we do covers both gas heaters and heat-pump heaters, and the diagnostic step is the same in either case: find the fault, then repair it. A heater that is diagnosed properly gets fixed for the right reason.

What to send about your heater

When your pool heater stops heating, the details you send make the first conversation faster. Write down the make and model of the unit, and describe what it is doing, whether that means no heat at all, heat that cuts out, or an error display. With that information in hand, we can quote the repair for your approval before any work begins, so you know the cost up front and decide from there.

One note on safety. A heater combines electrical parts with gas connections in a single cabinet, and opening electrical equipment yourself is not something we recommend. Leave the cabinet closed and let a trained technician handle the inside of the unit.

Once we have the model details and a clear description of the behavior, the next step is a proper diagnosis at your pool.

Why the fault comes before the quote

When a heater stops warming the water, the tempting move is to order a part and hope it was the problem. We work the other way around. Before anything is replaced, we diagnose the heater and find the actual fault. Only then do we quote the repair, and we wait for your approval before any work begins.

That order matters. A heater can fail in more than one way, and a guess at parts can leave you paying for a component that was never the issue. The diagnosis narrows things down, so the quote describes the fix your pool actually needs.

It also means you stay in control. You see what we found and what the repair will cost before a wrench turns, and nothing proceeds unless you say so. The fault comes first, then the quote, and the repair only starts with your approval.

Why we leave the cabinet closed

When a heater stops heating, it can be tempting to pop the cabinet open and look for the problem, or to crack open a pressurized filter to check something inside. We ask that you not do either. Heater cabinets contain electrical components, and a filter under pressure can be dangerous if it is opened the wrong way. Neither one needs to be opened for you to gather the information we describe in the other sections, so there is nothing to gain by taking that risk.

Leaving the equipment closed also keeps things simpler for whoever works on the heater next. Components stay where they were, nothing gets disturbed, and the picture we build from your description matches what is actually inside the unit. It is enough to observe, note what you can from the outside, and write it down.

Look, listen, and describe, but keep the cabinet shut and the filter sealed.

When replacement comes up instead

Sometimes the diagnosis points past repair, and the honest conversation becomes about replacement. That applies to a gas heater as well as a heat pump. Before anyone talks about a new unit, the comparison that matters is what it costs to run the equipment, given the way you actually use your pool. A heater that fits the pool but gets used differently than you expected can cost more over time than a different choice would have.

So when replacement comes up, we start with running costs rather than equipment names. The question is not which model sounds best in a brochure, but whether the equipment suits your pool and whether the cost of operating it matches your habits, your season, and your expectations for warm water.

That order keeps the decision grounded. If the numbers work for the way you swim, replacement is easier to commit to, and if they do not, you know why before anything is ordered.

Next step: pool equipment repair.

Where Sullivan’s works

Sullivan’s Pool Service maintains pools in and around Austin, including Northwest Hills, South Austin, West Lake Hills, Tarrytown, Great Hills, River Place, Crestview, East Austin, North Austin, West Campus, Hyde Park, Downtown Austin and St. Johns, and in Bee Cave, Cedar Park, Georgetown, Leander, Pflugerville and Round Rock. See every service area.

Weekly residential service has one fixed monthly price, set by pool size: see pool service pricing for what each size tier covers.