Need Advice: Mastertemp 400 Control Board Fried? (See pic)

[jubjub]

So, my Mastertemp 400 NG heater (built in 2010), which we rarely use here in FL, ignites, but then 3-4 seconds later shuts off and triggers a "Service Heater" light. I flipped the board over and did not observe any additional error lights. FWIW, the thermal regulator has a lot of corrosion (blue). I tried firing it up without the regulator as well as after I had baking soda'd the regulator, but same results (3-4 seconds on, then shuts off).

I'm thinking/hoping the control board is fried (see pic). It looks corroded, just like the thermal regulator. It has been over a year since I popped the heater case open. There was a LOT of debris (pine needles and leaves, etc.) wedged inside the case.

Thoughts?

If I had the $$$, I'd just replace the whole thing, but since we rarely use it, I'd rather keep it limping along for now.

Thanks!

 

[Arizonarob]

That IS a lot of corrosion, I suspect it might be the culprit. I’m not an expert in heaters, but I know someone who is. Hang tight.
@JamesW

 

[JamesW]

Sounds like it's not sensing the flame. Check the igniter. The igniter is also the flame sensor.

The corrosion is not good. I don't know that I would trust the heater to work properly without getting everything cleaned up properly.

If you're getting a lot of blue copper, I would be concerned that the heat exchanger is leaking and the combustion chamber is full of water.

 

[jubjub]

Sounds like it's not sensing the flame. Check the igniter. The igniter is also the flame sensor.

Is there a walkthrough you can refer me to on how to check the ignitor?

 

[JamesW]

Remove one of the bottom manifold bolts to see if water comes out. That will tell you if the combustion chamber has water in it.

 

[jubjub]

No water came out. They do look rusted, but no water.

 

[JamesW]

Check the igniter and replace if necessary.

Check the wiring connections on the Fenwal Ignition Control Module.

 

[JamesW]

On the Fenwal Ignition Control Module there is a red LED. If it is on steady, that indicates a control fault.

If it flashes 3 times, that means ignition lockout.

I suspect that the Fenwal Ignition Control Module is not getting flame rectification.

Flame rectification is where an AC voltage is sent to the flame sensor and when the flame connects the burner tray to the flame sensor, the flame carries current from the sensor to the burner tray.

Since the current only flows in one direction, the current is rectified into dc current.

The Fenwal Ignition Control Module measures the dc current to prove that a good flame is present.

Most likely, the Fenwal Ignition Control Module is not detecting the dc current.

This can be due to poor flame or a problem with the flame sensor/igniter, wiring or Fenwal Ignition Control Module.

The dc current is only 0.7 microamps to less than about 5 microamps.

The Fenwal Ignition Control Module has flame current test points labeled fc +/-.

If you have a really good multimeter that can check for dc current in the microamp range, you can check to see if the flame current is good.

Flame Current Measurement
Flame current is the current that passes through the flame from sensor to ground.

To measure flame current, connect a True RMS or analog DC micro-ammeter to the FC+ and FC- terminals.

Readings should be 1.0 µA DC or higher.

If the meter reads negative or below "0" on scale, meter leads are reversed.

Reconnect leads with proper polarity.

Alternately, a Digital Voltmeter may be used to measure DC voltage between FC+ and FC- terminals. Each micro-amp of flame current produces 1.0 VDC. For example, 2.6 VDC equates to 2.6 µA.

A good burner ground that matches the control ground is critical for reliable flame sensing.

 

[jubjub]

On the Fenwal Ignition Control Module there is a red LED. If it is on steady, that indicates a control fault.

If it flashes 3 times, that means ignition lockout.

I suspect that the Fenwal Ignition Control Module is not getting flame rectification.

Flame rectification is where an AC voltage is sent to the flame sensor and when the flame connects the burner tray to the flame sensor, the flame carries current from the sensor to the burner tray.

Since the current only flows in one direction, the current is rectified into dc current.

The Fenwal Ignition Control Module measures the dc current to prove that a good flame is present.

Most likely, the Fenwal Ignition Control Module is not detecting the dc current.

This can be due to poor flame or a problem with the flame sensor/igniter, wiring or Fenwal Ignition Control Module.

The dc current is only 0.7 microamps to less than about 5 microamps.

The Fenwal Ignition Control Module has flame current test points labeled fc +/-.

If you have a really good multimeter that can check for dc current in the microamp range, you can check to see if the flame current is good.

I ended up replacing the igniter with no improvement.
I then replaced the Fenwal with no improvement.
I finally replaced the thermal regulator, which did the trick.

I'm happy I bought a used $30 Fenwal on eBay instead of paying ~$170 for a new one.

Thanks to all who weighed in on suggestions. Hoping the control board hangs in there for a few more years.

 

[JamesW]

Ok, but the thermal regulator does not match the symptoms because the heater did not give a high limit LED error light and running without a thermal regulator did not help.

In any case, I'm glad that you got it working.

 

[jubjub]

Ok, but the thermal regulator does not match the symptoms because the heater did not give a high limit LED error light and running without a thermal regulator did not help.

In any case, I'm glad that you got it working.

The Fenwal flashed 3 times, which means ignition lockout. That's when I replaced the igniter and the Fenwal. Like I said, I thought that would have fixed it, but it was the regulator that did the trick. I am curious if you have any theory as to what was the actual cause.

 

[JamesW]

I think that there were probably two issues, the regulator and the igniter, or the regulator and the Fenwal.

Ignition lockout means that the Fenwal was not receiving or sensing the flame rectification signal.

I suspect that when you solved the flame rectification problem, the heater ran long enough to trip the high limit switch when the thermal regulator wouldn't open.