Hi, I'm Waldemar,
There can be few reasons why your spa is not heating neither filtering. Here is the most common problem:
Hi Limit Switch Trips (Heater Re-set Button)
Assuming that everything else is working properly (i.e. spa is set in the heater/filter cycle and water is flowing from the jets), the first thing you will look for is the Hi-Limit Switch, also referred to as the heater reset button. Now finding it can sometimes be a problem, it’s as if it was purposely put it in a hard to find place, especially in some of the older spas. NOTE: If you have a circuit board you will not see this hi-limit, please refer to "circuit board troubleshooting".
What you are looking for is a red button; it is the only actual part of the hi-limit switch that is visible without going inside the control boxes. When you locate it, give it a push, if you feel or hear a click, or you see a heater indicator light come on that wasn't on before, then you have solved the problem.
IMPORTANT: Some spas have the thermostats located on top. These are called Spa Side Controls, they have built in air buttons and orange indicator lights. One of the indicator lights says heater, this light comes on regardless if the spa is heating or not. Do not troubleshoot using this light, it could confuse you.
Why Does The Hi Limit Switch Trip?
The #1 reason is filter related. It has become old, dirty or clogged, which has restricted the flow of the water. This fools the hi-limit switch sensor into thinking that the spa water is getting to hot. This is what a hi-limit switch does. It’s a safety switch that measures water temperature, tripping if it senses a higher than normal heat rise.
A good way to check if the filter is causing the hi-limit switch to trip, is to run the spa without the filter for a couple of days. If the hi-limit switch does not trip, then it is time to buy a new filter.
Another reason the hi-limit switch trips is for the very reason they were designed; the spa water exceeded an abnormal temperature rise.
The final thing it could be, without getting further complicated, is the hi-limit switch is faulty and needs to be replaced.
Other things to look for:
Are all the jets open to allow maximum flow? Are the shut off valves open all the way? Is there enough ventilation where the equipment is? (Can equipment breathe?) Is there water coming out of the jets at all?
FINAL NOTE: Before you drain your spa, turn down the thermostat! By not doing this can cause the hi-limit switch to trip.
Let me know if it helps.