Pool Heater Not Working? What to Check, and Where to Stop

A pool heater that will not fire is frustrating, and it is also the one piece of pool equipment where guessing can genuinely hurt you. Gas, high voltage, and combustion are all involved. So this guide splits cleanly into two halves: the things you can safely check yourself in ten minutes, and the things where the correct action is to stop and call someone licensed.

Start here: it is probably flow

Every pool heater has a flow-related safety interlock, usually a pressure switch. Its job is to confirm that enough water is moving through the heat exchanger before allowing the burner to fire. Without that, the exchanger would heat with little or no water in it and destroy itself.

So a heater that will not fire is very often a heater correctly protecting itself from a flow problem somewhere else in the system. Check, in this order:

• Skimmer and pump baskets. Full baskets starve the pump. This is free to check and fixes a real share of no-heat calls.
• Filter pressure. A filter well past its cleaning point chokes flow. Compare against your clean baseline; if it is 8 to 10 psi above, clean it and try again. Our filter guide covers how to establish that baseline.
• Valve positions. Someone may have left a valve turned after vacuuming or backwashing, diverting flow away from the heater.
• Pump speed.This one catches a lot of people with newer equipment. A variable-speed pump running at a low, efficient filtration speed may not move enough water to satisfy the heater’s pressure switch. Many systems are programmed to step the pump up when heating is called for; if that programming is wrong or was lost after a power outage, the heater will simply never fire. Try running the pump at high speed and see if the heater lights.

The other safe checks

• Is it actually calling for heat? Set point above current water temperature, heater in the right mode, and if you have pool and spa set points, confirm you are adjusting the one you think you are.
• Power and gas supply. Check the breaker for the heater, and check that the gas supply valve is open. If other gas appliances in the house are also misbehaving, the problem is upstream of your pool.
• Read the error code. Modern heaters display one, and it is the most useful piece of information available. Look it up in your manual. If you call us, that code is the first thing we will ask for, and having it can turn a diagnostic visit into a single-trip repair.
• Look at the airflow.Leaves, nesting material, or debris blocking the heater’s vents or exhaust will prevent firing. Clearing debris from around the outside of the unit is safe. Opening it up is not.

Where to stop

The following are not DIY, regardless of what a video suggests. Gas appliances fail dangerously when they are worked on by people without the training and tools to test them properly.

Why scale shows up here too

A heat exchanger is a place where water is heated across metal surfaces, which is exactly the condition that encourages calcium to come out of solution. In our area, where fill water is moderately hard and evaporation concentrates calcium further with every top-off, an unbalanced pool will scale the inside of a heat exchanger over time. Scale insulates, so the heater works harder for less result, and eventually the restriction damages the unit.

This is one of the quieter reasons that keeping calcium and pH in range is worth doing properly rather than approximately. The chemistry that protects your tile is protecting the most expensive component on your pad at the same time. The ranges are in our water chemistry guide.

Gas heater or heat pump, in a North Texas winter

These fail differently and it is worth knowing which you own.

• Gas heaters burn fuel to make heat, so they work regardless of how cold it is outside and they heat quickly. They cost more to run per hour, which makes them a good fit for someone who heats the pool occasionally or heats a spa on demand.
• Heat pumpsmove heat from the air into the water rather than generating it. That is far more efficient, but it depends on there being usable heat in the outside air. As air temperature drops their output falls and their run times get much longer, and below a certain point they effectively stop being useful. So the common complaint that a heat pump “stopped working in winter” is often not a fault at all, it is the technology behaving as designed on a cold Texas morning.

If you would rather someone else sort it out

Our equipment inspection covers diagnosing heater problems, and our approach is the one we would want as a customer: find out what is actually wrong, tell you the cheaper fix before the expensive one, and be honest when something is beyond what we should touch. If your heater needs gas work, we will tell you that plainly rather than improvising, and we would rather send you to the right trade than guess with a combustion appliance in your backyard.