Domakihub Pool Heater Not Working? A Simple Troubleshooting Guide
Find the cause and the quick fixes before you call a technician.
Reviewed by Domakihub pool pros · 2026-06-23 · 5 min read
A pool that suddenly turns cold is frustrating, whether it is your own home, a holiday villa with guests arriving, or a hotel spa that has to stay warm. The video above shows a real heater being diagnosed step by step, and this guide gives you the same checks in plain order so you can spot the problem quickly. Most no-heat issues come down to a handful of simple causes you can rule out yourself before calling a professional.
Why pool heaters stop heating
Pool heaters fail to heat for a small set of common reasons: not enough water flow, a tripped breaker or interrupted power, a thermostat set too low, low gas or fuel supply, or a dirty filter starving the system. Many units include a built-in safety switch that simply will not let the burner fire if water is not moving fast enough or the temperature reading looks wrong.
Knowing which family of heater you have helps. Gas heaters fail differently from electric heat pumps, and heat pumps in particular need warm enough outdoor air to work well — a real consideration on cooler Greek spring and autumn evenings.
What you can safely check yourself
Plenty of no-heat situations are caused by something basic: a paused pump, a closed valve, a clogged filter, a low thermostat setting, or a recently tripped breaker. These are all safe to inspect and reset. Anything involving opening the heater cabinet, gas lines, igniters, or wiring is best left to a qualified technician.
Before you start, give the system time. After power loss or a filter clean, many heaters run a short delay or a self-test before the burner relights, so wait a few minutes before deciding it is broken.
How to troubleshoot a pool heater that won't heat
- 1
Confirm the pump is running and water is flowing
Almost every heater needs steady water flow to fire. Make sure the pump is on, the skimmer and pump baskets are not blocked, and all valves to and from the heater are fully open. No flow, or weak flow, is the single most common reason a heater refuses to start.
- 2
Check power, the breaker, and the gas or fuel supply
Look at the heater's main switch and the electrical panel — reset any tripped breaker once. For gas units, confirm the gas valve is open and the tank or supply is not empty. For heat pumps, make sure the dedicated circuit has power. If a breaker trips again immediately, stop and call a technician.
- 3
Clean or backwash the filter
A dirty filter chokes water flow and triggers the heater's flow safety, which can mimic a broken heater. Clean a cartridge filter or backwash a sand or DE filter, then restart the system. Restoring proper flow alone fixes a surprising number of no-heat complaints.
- 4
Set the thermostat correctly and check the mode
Confirm the heater is in heat mode and the target temperature is set above the current pool temperature. Some units have separate pool and spa settings, plus a timer or schedule — make sure heating is not switched off by a clock or a vacation setting you forgot about.
- 5
Read the display and look for an error code
Modern heaters show a code or a service light when something is wrong, such as low flow, ignition failure, high limit, or a sensor fault. Note the exact code, check it against the manual, and try one power cycle. If the same code returns, you have a precise clue to give your technician rather than a vague 'it doesn't work'.
Rather have a pro handle it?
Get a vetted pool pro in your city — one number, booked in EN/EL/DE.
FAQ
- My pool heater turns on but the water still feels cold. Why?
- This is usually weak water flow, a dirty filter, or a thermostat set too low — or simply not enough run time. Heat pumps especially heat slowly and need many hours, and they lose efficiency when the outdoor air is cool, so the water can stay lukewarm even though the unit is running.
- When should I stop troubleshooting and call a professional?
- Stop as soon as you face gas smells, water leaks, scorch marks, repeated breaker trips, or any error code that returns after a reset. Opening the cabinet, gas components, igniters, and wiring should always be handled by a licensed technician for safety and warranty reasons.
- Why does my heat pump work worse on cold mornings?
- Heat pumps pull warmth from the surrounding air, so their output drops as the outdoor temperature falls. On chilly Greek mornings in spring or autumn the heater runs longer for the same result, and below a certain air temperature it may struggle to keep up. A pool cover helps a lot by holding the heat you have already paid for.