I know this is an old thread but I had a recent related issue that may help some people.
I have the easytouch 8 and a STA-Rite SR400HD heater. The manual is a little confusing when it comes to the "external control" set up. Apparently there are 2 versions of external control. A 2-wire control (from the easytouch) or a 3-wire control from a pair of external relays (one for the pool and one for the spa).
What confused me was the Jumper 3 (JMP3) setting on the back of the heater control panel. The manual says:
If you jumper pin 2 and 3 (the default setting) "External Control Interface Circuit Disabled, Heater Membrane Pad Enabled".
If you jumper pin 1 and 2 "External Control Interface Circuit Enabled, "Pool On" and "Spa On" Keys Disabled. "OFF" Key on Membrane Pad Remains Functional"
Well I have an easytouch. That's an external controller, right? Well not really. Not when it comes to JMP3 apparently. It has to be set to jumper pins 2-3 or the heater will never come on.
It seems the easytouch's internal heater relay is wired to the heater's fireman’s switch in a way that requires the local heater controls to be enabled. That's seems odd to me because that setup uses AND logic to operate the heater. Both the easytouch AND the heater controller have to call for heat at the same time or the heater won't come on.
So if I have the easytouch set to 80 but the heater itself is set to 65, the pool will not heat (well not beyond 65). If the easytouch set to 80 and the heater is set to 100, the pool will heat to 80 (not to 100). When the easytouch switches to spa mode, its spa temp setting is used. So let’s say it's set to 104 but the heater itself is set to 100. The spa will only reach 100 (The local heater panel does not switch from pool to spa).
It seems like an odd setup to me but it works as long as you have the heater's local temperature set to something at or above whatever the easytouch is set to and hope no one messes around with the settings on the heater's panel.