I am using a product to find a small leak in the hot tub, but they told me to turn off the heat and keep the circulation going. How do I turn off the heat without turning off the tub?

These types of timers were used and are still used for many different devices. The dial represents the clock and you pull or push for the hours you want the device to run during the 24 hour clock. For a hot tub you will want circulation for at least 4 - 6 hours a day. To circulate but also to maintain the heat. With a good hot tub cover and good insulation inside the tub your circulating time would be less and save you some money. Hope that helps.

Water heater can be added to any incoming water line, either on hot or cold.
http://waterheatertimer.org/How-to-install-under-counter-water-heater.html
Under-counter water heater located near tub will supply hot water just like ordinary household water heater. But it will not reheat water that circulates inside the spa tub.
Otherwise, a spa heater is made with electric element that can work with 120V or 240V. Water from tub circulates through tank that holds element. Element must be fully immersed in water.
To retrofit spa tub with this heater would require cutting water line near pump, running both ends of water line into tank with element.
Then of course you would need to retrofit adjustable thermostat to control when element is on. And integrate element operation into air control switch at tub that can override thermostat so element is not heating when tub is not in use.
Unless there is a pre-packaged kit to retrofit heater, I think adding heater would be difficult.

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

Sounds like the heating element has gone out again. Once you reset the circuit breaker and the tub turns on it will start to circulate the water. This usually runs like this for about 2 mins and then the tub will recognize it is cold and send power to the heater. If the element is back at that point it will blow the circuit breaker.
If this circuit breaker pops as soon as you turn it on then you most likely have a bad circuit board.

Rod
www.uspartscenter.com

The problem is not your thermostat. It is the person who told you that your AC would be your sole source of hot water. The purpose of heat recovery is to ASSIST with hot water production and reduce the current used by your water heater. The only time your AC heats your water is when it is working to cool (or if it's a heat pump, cool and heat) your home. Turn your water heater back on and let your AC help keep the water hot. It's not supposed to do it alone.

A few things you may try before the expense of a heater core, and the labor putting another one in.
First, I just want to mention I have used Bardahl stop leak, and it worked very well for me, It's a good product. Also, you're right, the a/c commpressor is a seperate issue.

Now, you mentioned you changed the thermostat, the following test is just to make sure it's working properly, and to check the coolant circulation.

1. With the heater temp and blower off, start your vehicle and let it run 6 to 8 minutes to allow it to reach normal operating temperature. then;
turn your heat temperature and blower wide open, when you do, listen very closely in the engine compartment, you should hear a small click from the thermostat opening up to allow ciculation of the coolant.

2. Turn the engine off. Carefully reach behind the engine, at the fire wall where your inlet and outlet hose, ( both about 1 inch in diameter ),hook up to your heater core. feel each one of the hoses. If both are hot, then your coolant is circualting through the core. If only one of them are hot, then the coolant is being blocked from circulating through the core, and if that is the case I would probably try flushing the whole cooling system first.

I hope this helps.

you may have a system that uses a small circulating pump that circulates the water thru the heater to keep water temp at proper level (this is usually the case with hot springs spas and is because it is the most cost effective way to maintain constant water heat without using a full size pump or two speed pump just to push water past the heater core. therefore the issue is you have a problem with your jet pump and it has nothing to do with the circulating and heating portion of the spa. you can check to see if there are any reset buttons in or near the equipment as well as open enclosures to make sure everything is clean and dry also make use any contacts on spa skirting are secured propertly

Check to see if there are any screen type filter to the tub as debris may be clogging it. Also air lock can occur but it should not be causing problems as 90% clear them selves.....

MY control panel was replaced ,it cycles but, no lights ,no jets,no heat works..What's the problem .

Sounds as if the 'mode' for the tub is set to sense the temperature of the water. see if there is a setting on the control box to a 'timed' setting for filtering and heating instead of controlled by the temperature setting. the problem is the the control box is away from the water and when it calls for heat it is because the water is cooler there than in the hot tub. so when it calls for heat and the water starts to circulate it gets the hot water from the body of the hot tub and then shut down because it senses the 'hot water'. make sense?

You must keep your circulator pump running if you want the water to stay hot. The water is being heated inside the pipes but it isn't getting circulated until you turn on the jets pump.