Why will my pool heater not ignite?

Most commonly inadequate water flow — check the filter pressure and pump first. Beyond that, igniter faults, gas valve problems and flame sensor issues are the usual causes, at $250–$800 to repair.

My heater runs but the water is not getting warmer. Why?

Often a scaled heat exchanger reducing heat transfer, an undersized unit for the pool, or — on a heat pump — ambient air too cold for efficient operation. Confirm the thermostat setting and run time before assuming a fault.

Why does my heat pump not heat as well in cooler weather?

That is normal, not a fault. Heat pumps move heat from the air into the water, so efficiency falls as air temperature drops, and most units become impractical below roughly 50°F ambient.

What should I do if I smell gas near my heater?

Shut the gas supply off at the valve, keep ignition sources away, and call your gas utility from a safe distance. Do not attempt to diagnose or operate the heater until the utility has cleared it.

How much does it cost to fix a pool heater that will not heat?

Most repairs run $200–$900. A scaled or leaking heat exchanger is more, at $400–$2,500, and often makes replacement the better value on a heater over ten years old.

Pool Heater Not Heating

A heater that will not ignite and one that ignites but heats poorly are different problems with different causes. Both start with the same safe checks, and both stop well short of anything you should attempt yourself.

Diagnose My Pool Problem Pool heater repair

Is it urgent?

Rarely urgent in the sense of needing same-day attention, with one clear exception below. Most heater faults are a comfort issue rather than a safety one, and the pool remains fully usable unheated in the meantime.

What you can safely check

Photograph any error code. The single most useful piece of information for a technician, and it usually resolves the question before they arrive.
Confirm water is flowing. Most heaters refuse to fire without adequate flow. Check the filter pressure and confirm the pump is running normally.
Check the gas supply is on. At the valve only. If other gas appliances in the house have also stopped, the issue is upstream of the pool.
Check the breaker. Gas heaters still need electrical power for their controls.
Check the thermostat setting. It sounds obvious, and it accounts for a real share of service calls.
For a heat pump, check the outdoor temperature. Heat pumps lose efficiency as ambient air cools and become impractical below roughly 50°F. That is normal operation, not a fault.

Two different problems

Will not ignite vs. ignites but does not heat
Symptom	Likely cause	Repair
Will not ignite at all	Igniter, gas valve, flame sensor, or gas supply	$250–$800
Ignites, then shuts down	Flame sensor or a safety switch responding to poor flow	$200–$600
Runs but heats slowly	Scaled heat exchanger, undersized unit, or low gas pressure	$300–$1,200
No power to the unit	Breaker, transformer, or control board	$150–$900
Heat pump running but water stays cool	Refrigerant fault, reversing valve, or air too cold	$300–$1,500

PoolSavr planning ranges, national, including a service call.

What not to do

Do not open the combustion chamber. Gas components are technician-only.
Do not bypass a safety switch. It is preventing a fire or a destroyed heat exchanger, not being oversensitive.
Do not attempt gas line work. Including tightening a fitting.

How to read a PoolSavr estimate

Step 1
Instant estimate
Based on your project selections and general pricing assumptions. Useful for deciding whether a project is realistic.
Step 2
Measured estimate
Uses your pool, spa, or deck dimensions to price the work against the areas actually being resurfaced, tiled, or replaced.
Step 3
Contractor proposal
Prepared by a licensed professional after inspecting the site. This is the only number that becomes a contract.

PoolSavr is an estimating and matching platform. We do not perform pool work ourselves — licensed local professionals do. Contractors pay PoolSavr for qualified project leads, which is how the estimating tools stay free for homeowners. A PoolSavr estimate is a planning range, never a guaranteed quote — read thefull estimate disclaimer.

Frequently asked questions

Why will my pool heater not ignite?: Most commonly inadequate water flow — check the filter pressure and pump first. Beyond that, igniter faults, gas valve problems and flame sensor issues are the usual causes, at $250–$800 to repair.
My heater runs but the water is not getting warmer. Why?: Often a scaled heat exchanger reducing heat transfer, an undersized unit for the pool, or — on a heat pump — ambient air too cold for efficient operation. Confirm the thermostat setting and run time before assuming a fault.
Why does my heat pump not heat as well in cooler weather?: That is normal, not a fault. Heat pumps move heat from the air into the water, so efficiency falls as air temperature drops, and most units become impractical below roughly 50°F ambient.
What should I do if I smell gas near my heater?: Shut the gas supply off at the valve, keep ignition sources away, and call your gas utility from a safe distance. Do not attempt to diagnose or operate the heater until the utility has cleared it.
How much does it cost to fix a pool heater that will not heat?: Most repairs run $200–$900. A scaled or leaking heat exchanger is more, at $400–$2,500, and often makes replacement the better value on a heater over ten years old.

Ready to see what your project costs?

Start with the work you are considering. You will get a preliminary range before anyone asks for your phone number, and you decide whether to request a contractor review at the end.

Diagnose My Pool Problem