Mastertemp E05 unless switch membrane unplugged

[hambone]

I’ve got a weird one. Like the title says, I Mastertemp NG 400 that threw the E05 and first step was to replace SFS. I confirmed it was bad and got a new one but still got the E05.

I had issues with the switch membrane buttons not working so I ordered a new one.

While waiting for the membrane, i pushed the multi meter tips firmly into the harness on the control board to check values when it shuts off…

The problem is, it didn’t throw the error anymore with multi-meter attached and no front membrane plugged in. I’ve also pulled the thermal regulator out (as I was troubleshooting), water is 65 degrees and heat set to 85.

I plug in the new membrane (or the old one) and it throws E05…. I pull the mult-meter test pins out of the harness, it throws E05.

I’ve replaced nearly every sensor on this 1-2 times, as well as the heat exchanger that leaked and the combustion chamber that rusted.

I’m thinking this could be the board… but I’m not sure. This is my 4th heater in 16 years of being a pool owner (two of those were totally my fault).

 

[bradgray]

E05 is almost always the SFS. Are you sure the spade isn't crooked/missed the female terminal?

You say you're pressing pins into the harness. There are numerous that connect to the pcb. When reading I assume you are reffering to the display, but that would be reversed. The board is male and display is female. So I'm unclear.

Can you specify where you're pressing your probes?

 

[hambone]

Thanks for the reply. I believe my issue was the PCB board. Somehow the probes must have provided a resistance through my multimeter and provided readings that the board accepted temporarily. When I finally could get a keypad functioning the stack flue temp was reading zero (others reported 80/40), in my research.

I ordered a non-oem board on Amazon and everything works flawlessly (for now). I adjusted the flow with my variable pump and adjustable returns to determine the limits of where the heater would bypass and shutoff so I can get the heating scheduled with the cleaning and salt generator.

I guess I’ll wait for the gas valve, fan motor, and fenwal to fail so I can complete the entire rebuild/replacement of every item in this thing. What a learning experience!!!

The forum posts are priceless - thanks for all the posts.