Pool Heater Not Working? Fast Repair in Sudbury

* If you smell gas or suspect a leak, shut the system off immediately and call a professional. Gas-related issues are not something to take chances with *

If the thermostat is set too low or not calling for heat, it can seem like nothing is happening.

Pool heaters need proper water flow to run. A dirty filter, weak pump, or closed valves can stop the system from turning on.

Over time, burners and heat exchangers can get dirty or clogged. 

This can reduce performance or cause the heater to shut down. 

Blocked exhaust, poor airflow, or even strong wind can prevent proper operation and stop the heater from running. 

If it won’t start, it could be the pilot, igniter, or gas supply.

These are common issues, but usually need a technician to diagnose safely.

If your pool heater won’t turn on at all, the issue is usually something preventing it from starting, not necessarily a major failure.
In most cases, it comes down to power, water flow, or built-in safety controls stopping the system from firing. The key is understanding what’s blocking the startup.

NO POWER TO THE HEATER

If the heater isn’t getting power, it won’t respond at all. This can be caused by:

• A tripped breaker 
• The disconnect being switched off 
• Blown fuses or loose wiring 

If there’s no display or response from the unit, power is the first thing to check.

WATER FLOW PROBLEMS (MOST COMMON)

Pool heaters rely on proper water flow to operate safely. If flow is too low, the pressure switch won’t close — and the heater won’t start. Common causes include:

• Dirty or clogged filter 
• Debris in pump or skimmer baskets 
• Valves not fully open 
• Weak or failing pump 

Even small restrictions can prevent the heater from turning on.

IGNITION OR GAS ISSUES 

If the heater has power but won’t fire, the issue may be in the ignition system. Possible causes:

• Gas supply turned off 
• Dirty or blocked pilot assembly 
• Faulty igniter or thermocouple 
• Debris (like spider webs) blocking gas flow 

The system may try to start but fail to ignite properly.

SAFETY SWITCHES STOPPING STARTUP 

Pool heaters are designed with safety controls that prevent operation if something isn’t right. These can include:

• Pressure switch (low water flow) 
• High-limit switch (overheating protection) 
• Rollout or vent safety switches 

If any of these are triggered, the heater won’t turn on at all.

CONTROL OR ELECTRICAL PROBLEMS  

If everything else checks out, the issue may be internal. This can involve:

• Control board failure 
• Damaged wiring 
• Faulty relays or sensors 

These problems usually require proper diagnosis and repair.

ERROR CODES CAN POINT YOU IN THE RIGHT DIRECTION If your heater has a display, error codes can help identify the issue. For example:

• “FLO” or “LO” often indicates a water flow problem 
• Other codes may point to ignition, sensors, or internal faults 

Checking your manual or model online can help you understand what the code means.

HEATER NOT TURNING ON AT ALL?  

If your pool heater isn’t responding, something is stopping it from starting — whether it’s power, water flow, or a safety control.
Some issues are simple. Others require proper diagnosis to avoid bigger problems. Either way, guessing wastes time.
We’ll quickly pinpoint what’s stopping your heater and get it running safely again.