Hot Tub Not Heating to Set Point

[ViewMaster]

I have a Jacuzzi J350 series. After a water change the tub heated from 55 degrees to 82 degrees just fine.  For the last two days it has not heated to the 101 set point, but has maintained temperature at 82 degrees indicating that the heater is working.  The heater icon is showing on the topside control panel indicating it is calling for heat.  The small circulation pump is running pushing water through the heater.  The heater has 240 volts to the wire leads.  I am confused as what to do next. 

[Tman122]

I have a Jacuzzi J350 series. After a water change the tub heated from 55 degrees to 82 degrees just fine.  For the last two days it has not heated to the 101 set point, but has maintained temperature at 82 degrees indicating that the heater is working.  The heater icon is showing on the topside control panel indicating it is calling for heat.  The small circulation pump is running pushing water through the heater.  The heater has 240 volts to the wire leads.  I am confused as what to do next.

Temp sensor........

[Spatech_tuo]

I have a Jacuzzi J350 series. After a water change the tub heated from 55 degrees to 82 degrees just fine.  For the last two days it has not heated to the 101 set point, but has maintained temperature at 82 degrees indicating that the heater is working.  The heater icon is showing on the topside control panel indicating it is calling for heat.  The small circulation pump is running pushing water through the heater.  The heater has 240 volts to the wire leads.  I am confused as what to do next.

The fact your spa is heating to 82º does not necessarily mean your heater is working depending on how long it takes to get there. Heat from the circ pump will transfer to the water and can get your tub to that temp.

[ViewMaster]

Thank you for that response.  The tub is heating from the heat from the pump, as you say.  The heater was not coming on.  I confirmed 240 volts at the heater leg wires, but no heat.  I removed he heater and bench tested it with the same voltage and it worked, very hot for half a minute or so.  I reinstalled it and not heat when the circulation pump moved water thought the core.  However it heats when is disconnect the water feed through the stainless steel heater core.  I guess this heater should be replaced, but it is odd that it heats when dry, but does not when it is wet.  Has anyone else experienced this?

[SerjicalStrike]

Heaters are dumb.  They either work or they don't.  Is your spa in Standard mode?  There is a mode that only heats the water to within 20 degrees of the set temp.