Pentair MasterTemp 250 Flame Sensing

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mattb1963

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Sep 14, 2023
10
Spokane WA
Hello. Long time listener first time caller. My Pentair MasterTemp 250 tries to light off then flames out then enters ignition loclout. Have tried all the usual steps ie cleaned all electrical connections checked all switches and sensors. A trusted associate who maintains heating equipment for a living believes it is a flame sensing issue and after spending an hour with the heater he believes the flame is not being sensed due to something interfering with the flame itself ie some sort of obstruction or distortion in the flame box is causing the ignitor to not sense the flame then the ignition control unit shuts off the gas. Has anyone experienced this or something similar? Thank you in advance and please be kind.
 
JamesW said:
Did you check the flame current?
Click to expand...
Checked flame current and that led to the conclusion that, since igniter checked out and separate ground was rigged in it could be there is a problem the location. Or shape or size of the flame. Like something interfering between gas input and ignitor. Now I am wondering if maybe the ignition control module is kaput. Can't imagine what might be interfering with the actual flame itself.
 

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JamesW said:
What was the reading?

Check the gas pressure static and dynamic.
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The flame current is low, .63 and .75 milliamps where Fenwall says must be at least 1.0. Waiting for hose barb to arrive Monday to configure my new manometer to check static and dynamic pressure after the gas valve. Electrician out today believes it is not a power supply or grounding issue and not transient or stray voltage. Thank you in advance for any guidance.
 
mattb1963 said:
The flame current is low, .63 and .75 milliamps where Fenwall says must be at least 1.0.
Click to expand...
The current is in the microamp range.

Doublecheck your readings.

Are you reading microamps or volts?
mattb1963 said:
Waiting for hose barb to arrive Monday to configure my new manometer to check static and dynamic pressure after the gas valve.
Click to expand...
Check the pressure at the gas valve inlet, which is before the heater.
 
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.

If you don't have a RMS meter you can just test for voltage between FC+ and FC- terminals to confirm if you have flame sense.

Each micro-amp of flame current produces 1.0 VDC.

For example, 2.6 VDC equates to 2.6 µA.
 
JamesW said:
Was that static (heater not running) or dynamic (heater running)?
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Not running. The strange thing is 9 times out of 10 the heater will short cycle then enter ignition error lockout. Then the next time it works. Fires off and runs for hours. Then the next umpteen times lockout, then it will function correctly again. No discernible pattern or condition. Just seems arbitrary.
 

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