Heater has been working fine for past year since fixing gas flow issue (thank you to this forum for helping me troubleshoot and solve that issue). Now I am back for more advice. Heater does not fire and service heater led is on. Immediately after turning on power the PS led comes on, then a click and it goes out then HLS led stays on. Doesn't fire, no blower... Other than that first little click nothing happens. Looking at flow chart in manual it says if HLS is on and blower does not start then "replace control board". Does this sound like right diagnosis? Costly part for me to replace looks like about $300 so I want to make sure this is indeed the issue. Is the HLS sensor a simple on/off switch? I already tried to bypass it with a jumper no improvement light still on.
Mastertemp 400 service heater and HLS leds on
- Thread starter bobca1
- Start date
After looking at wiring diagram some more realized there are 2 sensors on the other side of manifold lower one is HLS. Jumped the lower one and heater starts and runs fine now. So I am ordering new HLS sensor from Amazon. I was jumping AGS sensor earlier which is on other side... While I'm at it going to go ahead and replace all 3 sensors. HLS, AGS, thermistor.
Please look at your thermal regulator as well. That sensor could be doing its job but leading you in a wrong direction. So double check your thermal regulator. Don't just swap out parts without knowing if they are truly bad.