De gas 100mj spa heater - Pool & Spa

error codes don't appear on millivolt units. LO for digital models is an open safety within circuit, most common being the pressure switch

Low flow. Try cleaning the filter.

F4 = bad igniter ... Has this heater worked in the past and just suddenly stopped? Look for a bad igniter.

High limit switches are very cheap 1 time switches. They do not go out without a reason. When is the last time the heat exchanger was flushed? Has the burner tray been cleaned recently?
Is there enough water flowing through the heater? Is the heater and pump set on a timer?
If you have a sand or DE filter, do you backwash frequently enough?

All these things will affect the temperature of the outgoing water and the temperature of the high limit sensor(switch). I would say it is most likely flow related, but could be that the gas valve isnt tuned up too.
I know this is not a solution, but hopefully it will help you to figure out what is going on.

If you have a sand filter you just backwash it. If you have a DE filter you need to backwash then recharge with the correct amount of DE.If you have a cartridge filter you will need to break it down pull the cartridge and hose it down. Check to be sure your baskets are clean also and check the impeller on the pump also. Clogs in your suction line can cause this problem also.

Your not getting enough pressure to run the heater. So you need to clean the strainers and clean the filter. If you have a DE filter you may want to break it down and clean it. While your at this you should check your pressure switch and your by-pass valve.

My pentair matertemp 400,000 BTU natural gas heater cycles on and off before reaching desired temperature. I completely cleaned the DE filter and flow should not be an issue. When running the spa the pressure is 25. When running the cleaning system (polaris pop ups) the pressure is 30. Burner fires for 80 seconds then shuts off, reignites after 53 ceconds.Any tips on what might be the issue with the heater

Manual. Try page 35 on down.

que clase de calento tiene modelo y marca

you have tear in DE filter cloth.