Heater runs but pool water does not reach set temperature; long run times with lukewarm water.

Safety: For gas or internal component checks, turn off power and gas. Basic performance checks can be done with the heater running.

Steps:

• Verify setpoint and mode: Confirm the thermostat is set higher than current water temperature and that the heater is in the correct mode (Pool vs Spa).
• Check pool cover: If the pool is uncovered, especially in windy or cool conditions, heat loss can exceed heater output. Use a solar or thermal cover to reduce loss.
• Confirm run time: Calculate expected temperature rise: many Lochinvar pool heaters raise water about 1–2°F per hour for a typical residential pool. If rise is much lower, suspect performance issues.
• Inspect burner flame: Through the sight glass, flames should be mostly blue with small yellow tips. Large yellow flames or lifting flames indicate combustion problems requiring a technician.
• Check for scale: Older heaters or those on hard water may have a scaled heat exchanger, reducing heat transfer. Symptoms include noisy operation and high limit trips. Descaling should be done professionally.

If the heater is undersized or gas pressure is low, consult a pool professional or gas technician to evaluate sizing and supply.