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Aquahot and Thermostat Function
I have fielded two events this week about this issue. So I am posting in a new thread to help find the info in a search engine. 

Here is the situation. The thermostat, when it calls for heat, puts out a 12v positive signal. The Aquahot unit, wants ground signal to turn on one of the zones. 

This is accomplished in a rather clever way. If you have this setup, you will find a couple of automotive style relays attached very close to the terminal strip on the Aquahot. The purpose of those relays is to turn the 12V positive from the thermostat into a ground signal for the zone on the Aquahot. 

How does this magic happen?


(Corrected version)

The 12V positive signal from the thermostat is fed into terminal 85. Terminal 86 is grounded to the ground lug on the Aquahot. When 12 v is applied the relay closes. 

When the relay closes, terminals 30 and 87 now make contact. Terminal 87 is also connected to the ground lug on the Aquahot. Terminal 30 is connected to the input terminal on the Aquahot strip that activated the zones. When the relay closes, there is now a ground pathway from the terminal strip to ground. And the Aquahot zone, pumps and fans should activate. 

If you suspect a problem, the easy diagnostic looks like this. Activate the heat at the thermostat. Wait three minutes or so for the Tstat to turn on. Measure the voltage at terminal 85. It should read 12v positive. If it does not either there is a problem in the wiring or the thermostat. 

If you have 12 positive at the terminal 85, but still no pump running, then make a jumper and run it from the Aquahot terminal strip terminal for the zone you are working on to GROUND. Remember the AH wants a ground signal. If the pump activates, you likely have a bad relay.
Richard and Rhonda Entrekin
99 Newell, 512
Subaru Outback Toad
Inverness, FL (when we're home Cool )
Richard,  could you have your terminal designations mixed up?  I think 85 & 86 are the coil and 30 is common with 87 being NO and 87a being NC.   

The thermostat should activate the coil.
Gordon Jones
Yes I do, Thank you for catching that. I will correct in the explanation.
Richard and Rhonda Entrekin
99 Newell, 512
Subaru Outback Toad
Inverness, FL (when we're home Cool )

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