Heater runs but pool water does not reach the set temperature or heats very slowly.

Safety first: Turn off power and gas before adjusting internal components. Do not modify gas orifices without a licensed gas technician.

• Verify setpoint and mode: Confirm the thermostat is set higher than current water temperature and that the correct mode (pool/spa) is selected.
• Check bypass and valves: Ensure most of the return flow is routed through the Thermeau heater, not around it. Adjust any manual bypass valves to increase flow through the unit.
• Inspect filter and flow: Clean filters and baskets to ensure adequate flow. Very low flow can reduce heat transfer.
• Evaluate heater sizing: Compare the heater’s BTU rating to pool volume and desired temperature rise. An undersized heater will heat slowly, especially in cold or windy conditions.
• Check for scale: If performance has declined over time, internal scale may be insulating the heat exchanger. Schedule a professional chemical descaling of the Thermeau heat exchanger.
• Gas pressure check: Have a gas technician verify that supply pressure and orifice sizing match Thermeau specifications.