Master Temp 400k BTU (HD) E05 error

[fitness jockey]

I've been scratching my head over this for a week now. I have 2 400k pool heaters for my pool. They both worked fine over the summer. Last year I had to replace the SFS sensor on one of them. The same one, a year later almost to the day, started acting up again. It starts heating, sometimes the flue temp goes up, sometimes it stays at 40. After a couple minutes the units shuts down. I have the temp set 2 degrees higher than water temp. Error E05 displays. The manual for the unit isn't the correct manual for diagnostic. I only have 1 led light that lights when heating, manual shows 3 lights, service heater, service system, heating. Can someone please give advice on how to troubleshoot and repair this unit? It is a year old.
Thank you,

 

[1poolman1]

I've been scratching my head over this for a week now. I have 2 400k pool heaters for my pool. They both worked fine over the summer. Last year I had to replace the SFS sensor on one of them. The same one, a year later almost to the day, started acting up again. It starts heating, sometimes the flue temp goes up, sometimes it stays at 40. After a couple minutes the units shuts down. I have the temp set 2 degrees higher than water temp. Error E05 displays. The manual for the unit isn't the correct manual for diagnostic. I only have 1 led light that lights when heating, manual shows 3 lights, service heater, service system, heating. Can someone please give advice on how to troubleshoot and repair this unit? It is a year old.
Thank you,

Only the heating LED will be lit if the heater is heating. The others are errors, indicating where to look if the heater doesn't light. Check the back of the board the next time it doesn't light, the SFS LED should be lit if you see E05.
Do you feel heat from the exhaust when the temp is reading 40? If so, it is either the SFS or the board. I have replaced 6 SFS in the last three months for some reason, one on a heater as new as yours just two weeks ago. I now keep two or three generic ones on my truck, they're about $15.00 online at Amazon. Never had a problem with one. Cheaper than replacing a board or getting an OEM SFS, good place to start.