HottuBitsFixed

since you have already replaced both m7 sensors this may be a stupid question. have you made sure that the pump that runs throught the heater is running and if so the the water is flowing

The most common solution to the three dots of a Gecko System as you know is low flow (pressure Switch} The hi-limit sensor will also throw the three flashing dots as well. that means that foe some reason the tub tub has overheated in the tub or the heater casing( where the sensor is attached) has picked up a temperature above a safe level. Reset the tub and let the heater power on. safely put one hand on the heater casing and one hand in the tub. the heater casing should feel the same as the water in the tub. if the casing is hotter then you have a restriction. try looking in the suction side of the pump to see if their is debris being you say the filter is good. If the temp of casing and water in tub feel the same then the hi limit may be coming from heater relay on the board not opening when it needs to shut the heater off. When it gets to this point you really need a voltage meter or amp clamp to specifically diagnose. let me know if this helps or you need further help

A DRY code implies that their is no water movement thru the heater. since you say the water level is at the right level. the first thing I would check is to see if the circ pump is running. you can find by tracing the plumbing from the heater to the attached pump. that will be your circ pump. You should be able to hear the pump running ( when the tub isnt in dry mode) If not running the you have a problem with the pump. reply back and I will diagnose further. If you do hear the pump running then I would next remove the filter and see if the code goes away, if it does go away. then your filter is too dirty to move ample enough water thru the heater. I would clean or replace filter and re install. If the code persist then you are prolly in an air lock. you can remove the airlock by powering down the tub and removing the suction side union and letting the water flow backwards for a second or so and then re install. also check while tub is powered off and suction plumbing is removed from pump. that debris isnt stuck inside the pump. you can feel with your finger or by looking inside. hope this helps

You have a temp sensor that is located inside your filter housing. If you are standing on the outside of your tub looking down into your filter housing, look to the left you will see a plastic looking nut/sensor. this is you temp sensor. you also have a hi-limit sensor that is located on the heater itself. this sensor is what gives the overheat msg. the main purpose of this sensor is to shut the tub off in case something fails to shut the heater off. A Sundance should not overheat at 105 degrees. An overheat is usually detected at 110 degrees. It sounds to me that you may have a fault in the hi limit sensor. This answer is provided from the symptoms you described. I am new to repairing hottubs and i am still best being in front of one to diagnose specifically what the problem is, so I hope the little I have stated has helped. See Sundance wiring diagram page 34 for more help http://www.sundancespas.com/Communications/InstructionManuals/05780Man.pdf