Last Updated: June 2026
You know what’s great? Craving a swim, walking out back, and dropping into water that’s already warm.
You know what isn’t? Hitting the switch and getting nothing.
A pool heater that won’t turn on is one of the most common problems pool owners run into, usually right when you’re opening the pool for the season. It’s inconvenient, but it’s rarely unfixable. Sometimes the fix is as simple as cleaning a filter. Other times it takes a little more digging.
Either way, whether you’ve got a heat pump, electric, gas, or solar heater, this guide walks you through it step by step. We’ve repaired thousands of pool heaters, so these are the same checks our techs start with.
Need help from a pro?
Get started with live pool heater troubleshooting, or call us for a free phone diagnosis at (407) 786-0000.
What to do when your pool heater won’t turn on
Start here: check the power
Before you touch anything else, check the simple stuff. It’s the fix more often than people expect.
- Walk to your breaker panel. If the breaker is tripped, flip it fully off, then back on
- Check for a blown fuse
- If your heater is on a GFCI outlet, press reset
- Make sure any heater power switch is set to on
If the heater fires up, you’re done. If not, keep going.
Check the filter
No matter what kind of pool heater you have, the filter is the best next stop.
Your heater relies on a steady supply of water. If it doesn’t get enough, at enough pressure, it usually won’t power on at all. And if it does, it’ll shut right back off. (Here’s why proper water flow is so essential for your heat pump.)
Here’s how to keep the water moving:
- Keep your filter and filter media clean
- Empty your skimmer and pump baskets weekly
- Run your pump at least 8 hours a day
Clear pipes mean steady pressure, and steady pressure is exactly what a heater needs to run.
Helpful cleaning and replacement guides: Cartridge filter | DE pool filter | Sand pool filter
Check the pool pump
If it’s your first time running the heater, there’s a chance your pump isn’t strong enough to deliver water at the pressure the heater needs.
Most of the time the fix is upgrading to a variable speed pool pump. But only go there after you’ve worked through the rest of this guide.
Related: Why you should upgrade to a variable speed pool pump
Double check the plumbing valves
It sounds obvious, but one valve turned the wrong way can cut water to the heater. And no water means no heat.
Take a quick walk around your equipment pad and make sure every valve feeding the heater is open and moving water.
Heater turns on, then shuts off?
If your heater starts up but cuts out a minute or two later, that’s short-cycling, and it’s almost always a flow or safety issue:
- Low water flow. Same culprits as above: dirty filter, closed valve, clogged basket. Clear them first
- Pressure switch. This part confirms the heater is getting enough water. If it’s faulty, it can shut the heater down even when flow is fine. A tech can test it
- High-limit switch. This shuts the heater off if it overheats. If it’s tripping or failing, the heater won’t stay on
If flow looks good and it still cycles off, the pressure or high-limit switch is the likely cause, and that’s a good point to call a pro.
My heat pump pool heater won’t turn on
Seeing an error code?
Many heat pumps flash a fault / error code instead of just refusing to start.
Check here to find what those error codes mean for your pool heater: Hayward, AquaComfort, Pentair, Raypak, AquaCal, Heat Siphon, or Gulfstream.
Damaged or weak electrical connection
If your heat pump isn’t getting the power it needs from the breaker, it won’t start. And if it worked before but suddenly won’t, a damaged connection is a strong suspect.
- Check that the heat pump is getting adequate power (usually 24 volts, depending on size)
- Inspect the wiring for tears or loose connections
- Check the wiring terminals for corrosion
Low water flow
As covered above, low flow from a blockage will stop a heater from starting.
- Clean your filter
- Empty the baskets
- Make sure the pump is sending enough water
Defective pressure sensor
A bad pressure sensor can’t detect water, which usually triggers a shutdown.
- Have a technician test the part to see if it needs replacing. Replacing worn parts quickly is the most cost-effective way to extend your heat pump’s life
Dirty heat exchanger
This is the part that transfers heat into your pool water. If it’s dirty or corroded, it can trigger a shutdown and sometimes block startup.
- Have a pro inspect it to see if it needs cleaning or replacement
Related: When to service your pool heat pump
Doing some heat pump troubleshooting? Check out these pool heater repair tips.
My gas pool heater won’t turn on
A quick note: Medallion Energy services electric and heat pump pool heaters, not gas units. The steps below are DIY guidance for gas heater owners, shared to help you troubleshoot.
Gas valve
Inspect the heater’s gas valve and make sure it’s set to open.
Gas supply valve
Same logic. Walk to your gas supply and confirm its line valve is also set to open.
Pilot light isn’t lit
Relight it per your manual, or see this gas pilot guide.
NOTE: The next three checks involve bypass testing, which means opening the heater. If you’re not confident doing this safely, stop and call a professional.
Heater switch
- Make sure the switch is set to on
- Bypass the switch with a jumper wire across both terminals. If the heater turns on, the switch needs replacing. If not, move on
Thermostat
- Set the thermostat higher than the pool water temperature
- Use a multimeter to check if the thermostat is getting power
- Use a jumper wire to bypass test it
High limit switch
This part shuts the heater off if it overheats. On most units it sits near the heater’s outlets.
- Bypass the high limit switch. If the heater triggers, replace it. Your heater may have more than one, so test both
My electric resistance pool heater won’t turn on
Electrical supply
If your electric resistance heater won’t start, check the electrical supply first.
- Check that the breaker is sending proper voltage
- Inspect the wiring for damage
- Check the wire terminals for rust or corrosion
Thermostat
Like gas heaters, your electric heater’s thermostat has to be set at or above your water temperature.
- Set the thermostat higher
- If nothing happens, use a multimeter or jumper cables to test it
Burnt out heating element
If you refilled your pool recently but forgot to power down the electric heater while the water was low, it may have burnt out.
- Call a professional to inspect for damage and any needed replacements
My solar pool heater won’t turn on
A solar heater can’t really be “turned on,” since the heating comes from the solar panels. But it’s still powered by your pump, so a few things can stop it from working.
Lack of direct sunlight
- Wait for the sun (we wish we were joking)
- If it is sunny, and if possible, move the panels to a spot with better exposure
Weak pool pump
Depending on your setup, the pump may need to push water up to the roof and back. Smaller or worn pumps sometimes can’t handle it.
- Check the PSI on your filter’s pressure gauge for proper levels
- If you have a variable speed pump, turn up the speed
- Upgrade to a stronger pump if needed
Curious about solar? Compare heat pumps and solar pool heaters.
When to call a pro
Worked through everything and still no heat? It might be time for a pool heater repair, or in some cases a replacement. If you’re weighing replacement, it’s worth knowing the cheapest ways to heat your pool before you decide.
But you don’t have to figure that out alone. Medallion Energy is EPA 608 certified and licensed (CPC056806), with thousands of pool heater repairs behind us and a 98% satisfaction rate. We start every job with a free phone diagnosis, so you get answers before you ever book a visit.
If you own a heat pump and like the DIY route, live pool heater troubleshooting might be the perfect fit. Otherwise, we’re a call away.
Call (407) 786-0000 for a free phone diagnosis.
Frequently asked questions
Why won’t my pool heater turn on?
The most common reasons are a tripped breaker, low water flow from a dirty filter or closed valve, or a thermostat set below the water temperature. Start by checking the power, then the filter and valves, before moving to heater-specific parts.
Why does my pool heater turn on, then shut off right after?
That’s short-cycling, and it’s usually a flow or safety issue. Low water flow, a faulty pressure switch, or a tripping high-limit switch are the usual causes. Clean the filter and open all valves first. If it keeps cycling, have the switches tested.
Can a dirty filter really stop my pool heater from turning on?
Yes. Pool heaters need steady water flow at the right pressure. A clogged filter starves the heater of flow, and its safety system will keep it from starting or shut it down quickly.
My pool heat pump has power but won’t turn on. What’s wrong?
If power is reaching the unit but it won’t start, look at water flow, the pressure sensor, and the heat exchanger. A damaged electrical connection or corroded terminal can also be the culprit even when the breaker is on.
What is a pool heater pressure switch and why does it matter?
The pressure switch confirms enough water is moving through the heater before it fires. If it’s faulty, it can stop the heater from turning on, or shut it down, even when water flow is actually fine. A technician can test it quickly.
My gas heater’s pilot light is on but it won’t fire up. What now?
Check that both the heater’s gas valve and the main gas supply valve are set to open. If the pilot is lit and gas is flowing but the burner won’t ignite, the issue is often the thermostat, heater switch, or high-limit switch.
Should I troubleshoot my pool heater myself or call a pro?
The basics are safe to DIY: checking the breaker, cleaning the filter, opening valves, and setting the thermostat. Anything involving opening the heater, electrical testing, or gas should go to a professional. When in doubt, a free phone diagnosis can tell you which it is.
How much does pool heater repair cost?
A “won’t turn on” repair typically runs $200 to $500, depending on the part. Most pool heater repairs fall between $200 and $800. Major work like a compressor or heat exchanger can run $1,200 to $2,500 or more. Service calls in Florida usually run $100 to $250, but Medallion starts with a free phone diagnosis. You always get a written estimate before any work begins.