thank you for this information, I'm having trouble getting the heater to ignite right now without the service light coming on.Check the stack flue temperature with the thermal regulator in and then out.
While running, press and hold the On button will display the exhaust temperature display.
Here is what the normal exhaust temperature should be:
Below 250 degrees...very low
250 to 290 ..................low
290 to 350.................acceptable
350 to 480 ..................high
Note: HD models can be up to 75 degrees higher. HD models use a cupro nickel exchanger and the efficiency is slightly lower resulting in less heat transfer and more waste heat.
If the exhaust gas temperature is higher than normal then water may be bypassing the heat exchanger through a broken bypass valve.
If you hold down the "pool on" button, it stays on 80, and then flashes to 40, then back to 80, and then the 80/40 reading and E05 indicate that the board is not getting a reading from the sensor. It's usually a bad sensor or damaged wires.
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If you undo the union, this part will unscrew so that you can get a better look into the inlet.
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Maybe the heat exchanger is scaled on the inside or sooted on the outside.
Before the service light comes on the heating light blinks and blinks, the digital temp goes from 80 to 180 to 0 and 80 flickerings constantly.
I will check the rest of the items you listed.