Balboa · VS / GS series (M7 heater)Fix soon

HFL on a Balboa hot tub: heater flow reduced

The two sensors in the heater are reading too far apart, which usually means water is moving through the heater too slowly. The heater shuts off but the tub keeps running.

Also shown as: HL, HtL, heater flow

Most likely causes

  1. 1Dirty or clogged filtermost likely
  2. 2Low water levelcommon
  3. 3Air lock after a drain and refillcommon
  4. 4Too many jets closed or a partly closed valveless common
  5. 5Weak pump or worn impellerless common

What to try, in order

  1. Top up the water to the normal level.
  2. Turn off power at the breaker, pull the filter, rinse it well, and put it back.
  3. Open all the jets so the pump is not pushing against closed fittings.
  4. If you just refilled, bleed air from the pump by pulsing it between speeds for 10 to 15 seconds at a time.
  5. Press any button to reset. The heater should restart within a minute or so if flow is good.
  6. If HFL keeps coming back, replace the filter if it is over a year or two old.

HFL questions

Can I use the hot tub with HFL on the display?

Yes, but the heater is off while the code shows, so the water will slowly cool. Clean the filter first. That fixes most HFL codes.

What happens if I ignore HFL?

After five HFL events in 24 hours the system shows LF and locks the heater out until you reset it by hand. In cold weather that can lead to a frozen tub.

Related codes

Balboa -- · Temperature not yet knownBalboa CHEK PH · Maintenance reminderBalboa CLN FLTR · Filter reminderBalboa CNFG FAIL · Configuration errorBalboa dr · Heater may be dryBalboa dry · Heater is dryBalboa Ecn · Economy modeBalboa FLO · Low water flow

General guidance. Follow your manufacturer's instructions; anything inside the control box is work for a licensed professional. Updated October 5, 2026.