Think of a low-flow message as a successful safety response, not as the nuisance itself. The heater is declining to add heat when water movement appears insufficient. The task is to find the circulation restriction or configuration change while leaving the heater’s protective devices alone.
Think of a low-flow message as a successful safety response, not as the nuisance itself. The heater is declining to add heat when water movement appears insufficient. The task is to find the circulation restriction or configuration change while leaving the heater’s protective devices alone.
Follow the water path
Start at the pool. Is the water level high enough for the skimmer to draw steadily? Are skimmer baskets packed with leaves? Is a suction cleaner or recently installed accessory affecting flow? Move next to the pump: with the equipment operating normally, is the pump basket filled with water or visibly pulling air?
Continue to the filter. Compare its pressure reading with the clean baseline recorded for this exact system. A higher reading can support a restriction diagnosis, but pressure varies widely among pools. Clean or backwash only according to the filter manufacturer’s process, with the pump off and all pressure released before opening any housing.
Finally, look at user-operated valves and return flow. A valve left partly closed after maintenance, a solar-heating change or a water-feature schedule can alter the route through the heater. If labels are unclear, photograph the positions and call the installer rather than experimenting.
Variable-speed pumps deserve a schedule check
A system may heat normally at one speed and fault after the automation reduces RPM. The correct solution is not to adjust the pressure switch. It is to have a qualified person confirm the heater’s required flow and program a compatible pump speed, considering filters, valves and plumbing resistance.
What not to do
Do not jumper the flow or pressure switch, bend contacts, increase pump speed beyond equipment limits, run a dry pump or open a pressurized filter. Do not assume the switch is defective simply because it is open; it may be reporting the exact condition it was designed to detect.
When service becomes the efficient choice
Call a pool professional if accessible baskets and normal filter care do not restore flow, if the pump loses prime, if air repeatedly enters the system, if valves are unclear or if the warning persists at a previously proven pump setting. Heater-internal tests and switch adjustments belong to a qualified heater technician following the model service manual.
Frequently asked questions
### Will a dirty pool filter stop the heater?
It can. A restricted filter may reduce flow below the heater’s operating requirement. Use the filter’s own gauge baseline and manual rather than a universal pressure rule.
Can I turn up my variable-speed pump?
A temporary change within the pump’s documented operating program may help identify a schedule-related pattern, but permanent settings should meet the heater and plumbing requirements without exceeding equipment limits. Ask the installer when uncertain.
Does low flow mean the pressure switch is bad?
Not necessarily. The switch may be responding to low circulation, valve routing or system pressure. Replacing or adjusting it before confirming flow can miss the cause and create a safety risk.
Why did the warning appear after filter service?
Possible reasons include a valve left in a different position, air not fully purged, a reassembly issue or a changed system restriction. Stop if there is leakage or trapped pressure and revisit the filter’s manual or service provider.