Heater problems arrive at the worst time: a cool evening, guests coming, the spa cold. Before calling for service, there is a short list of things to check in order, because most no-fire situations are caused by something outside the heater. Here is the sequence.
1. Is it being asked to heat?
Check the mode and the set temperature on the heater and on any automation system. A heater in spa mode will not heat the pool; a thermostat set below the water temperature will not fire. Automation schedules can also disable heating at certain hours. It sounds obvious, and it is the answer more often than anyone admits.
2. Is there enough flow?
Every heater has a pressure or flow switch that prevents firing when water flow is too low. Low flow is the most common cause of a heater that will not start or that short-cycles. Check:
- Filter pressure. A dirty filter restricts flow. Clean or backwash it. Filter cleaning without guessing covers when and how.
- Baskets. A full pump basket or skimmer basket starves the pump.
- Valves. A valve partly closed, or in a position that bypasses the heater, cuts flow.
- Pump speed. On a variable-speed pump, the low-speed filtration setting may be below what the heater needs. The schedule should bump the speed during heating.
- Air in the system. A pump that is not fully primed moves less water. Pump priming and air leaks works through that.
3. Is there gas?
For gas heaters: is the gas valve at the heater open? Is the propane tank empty? Is the house gas on? Did anything change, like a new appliance, that could overload the meter? A heater that lights and dies, or that heats weakly, often has a supply problem rather than a heater problem. Gas lines for pool heaters explains meter and pipe sizing.
4. Read the error code
Modern heaters display a code or a light pattern that names the fault. The manual, or a search for the model and code, tells you whether it points to flow, ignition, a sensor, a high-limit trip or a control fault. A high-limit trip usually means flow; an ignition fault means the heater tried and could not light, which points to gas, the igniter or the burners; a sensor fault is a part.
5. Power and controls
Check the breaker for the heater. Check that the pump is running, since many heaters will not respond without it. If the heater is controlled by an automation system, check that the connection is live and the heater is enabled there. A power cycle, once, clears some faults.
6. Ignition
If a gas heater clicks and does not light, or lights and drops out, the igniter, flame sensor or burner tray may be dirty or failing. Spiders and debris in the burner area are a real thing in the Piedmont after a winter off. These are technician items. Do not open the burner compartment beyond what the manual describes.
Heat pumps specifically
A heat pump is not broken because it will not heat on a cold morning. It extracts heat from the air, and output falls as air temperature falls; below its operating threshold it stops. It also needs airflow around it, so leaves, mulch and a fence too close cut performance. And it heats slowly by nature, so a cold pool takes days, not hours. If a heat pump runs but the pool is not warming, check air temperature, airflow, run hours and whether a cover is on. Heaters and the NC swim season covers what each type can and cannot do here.
Slow heating with a working heater
Heater fires fine, pool warms slowly. Usually the pool is uncovered and losing heat as fast as it gains it, or the heater is undersized for the volume, or the run hours are too short. A cover is the cheapest fix. Sizing a pool heater explains the math.
When to call
If flow, gas, power, mode and a single reset are all confirmed and the heater still faults, it is time for a technician. Ignition components, gas valves, control boards, heat exchangers and refrigerant are not owner repairs. Have the model and the error code ready; it shortens the visit.
Preventing the call
Keep the filter clean. Keep the equipment pad clear of leaves and mulch. Run the heater briefly each month in the off-season so it does not sit. Have it serviced before the spring heating season. Most heater failures we see had warning signs a season earlier.
We install and size heaters on pools across the Triad, including Kernersville and Randleman. Reach out if you are building a heated pool or upgrading the equipment on an existing one.