Pentair Mastertemp 250 will not stay lit. It lights, but Shuts off after five seconds. Ignition Error message

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M

mpmillermg

Member
May 3, 2025
8
Saint Rober, MO
Pool Size
20000
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
CircuPool Core-55
I have a Pentair MasterTemp 250 LP and I am having a Ignition Error when trying to turn the heater on the pool. I have had the heater going on four years, it worked fine last year and once
I opened the Pool this year it worked one or two days and now it will not stay on. I have troubleshot just about everything I have read that can give you and ignition error. When I turn the heater on the blower comes on, and then you hear a click and the rumbling sound of the igniter igniting the gas. Heat comes out of the exhaust for about 5 seconds and then shuts off, the heater cycles this like three times and then quits and shows the error code.

1. I checked my propane level in the tank and it is at 40%.
2. I replaced the air flow switch.
3. I replaced the ignition control switch.
4. I bypassed the AGS and high limit switch with a jumper and still got the error.
5. I checked the igniter with my ohm meter and it read at 96ohms so it is still good.
6. I tested the gas pressure coming into the inlet side of the gas control valve with an analog manometer. It started off at about 10in./wc before I turned the heater on, when the heater lights it drops to about 4 in./wc and when the heater shuts off the pressure goes up to about 15 in./wc. Then the heater will try to light again and it will drop to about 4 in./wc . I read its not suppose to drop more than 2 or 3 in./wc when it lights but it still should stay on right, just burn rich.
6. I tested the gas pressure on the manifold side(see video) below it does not drop to a negative reading when it fires up.
Any help with this would be greatly appreciated.
 
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MP,

Welcome to TFP. Sorry you have to find us with this problem. We've seen this a LOT and it can be frustrating. Seems to happen with all brands at some point and it can be very frustrating to nail down. Random replacement of parts is expensive and mostly just wastes money with no benefit. You seem comfortable with basic diagnostics are you comfortable opening it up to find the Fenwal ignition control module? Find it and let us know how many times it blinks. There are a couple things this can point us to.

Thanks.

Chris
 
Welcome to TFP.

I suspect you have a propane gas pressure problem. 4” WC is the minimum gas pressure and if it drops to that when running and flames out then you have a gas service problem.

You say your propane tank is 40% but some folks have discovered their gas gauge was broken.

Fill your propane tank and see if you get increased gas pressure.
 
setsailsoon said:
MP,

Welcome to TFP. Sorry you have to find us with this problem. We've seen this a LOT and it can be frustrating. Seems to happen with all brands at some point and it can be very frustrating to nail down. Random replacement of parts is expensive and mostly just wastes money with no benefit. You seem comfortable with basic diagnostics are you comfortable opening it up to find the Fenwal ignition control module? Find it and let us know how many times it blinks. There are a couple things this can point us to.

Thanks.

Chris
Click to expand...
Thanks for the quick reply Chris, I know that light you were talking about on the Fenway ignition control module. I have a different model of control module that does not have that light. I attached a picture of the model I have. You can see where there is the red blinking light is supposed to be is a chord that goes up to the panel. Mine will give you the error on the display and the only error I get is an ignition error.
 

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ajw22 said:
Welcome to TFP.

I suspect you have a propane gas pressure problem. 4” WC is the minimum gas pressure and if it drops to that when running and flames out then you have a gas service problem.

You say your propane tank is 40% but some folks have discovered their gas gauge was broken.

Fill your propane tank and see if you get increased gas pressure.
Click to expand...
Ok Ajw, I was thinking the same thing since it worked when the tank was at 60% at the beginning of the season? Can I increase the pressure myself on the gas gage, I seen where you do, I just don’t want to break anything or blow myself up of course.
 
mpmillermg said:
Ok Ajw, I was thinking the same thing since it worked when the tank was at 60% at the beginning of the season? Can I increase the pressure myself on the gas gage, I seen where you do, I just don’t want to break anything or blow myself up of course.
Click to expand...
Just fill the tank.

A liquid propane tank takes thermodynamics to change it to gas and develop gas pressure. You cannot simply turn the pressure up.

The tank needs to be full enough to absorb heat fast enough from the air or ground (if it's buried) to boil the liquid propane in the tank to a gas. In the warmer months this is rarely ever an issue unless a tank is grossly undersized.

You have issues with your LP tank sizing or installation not creating enough gas pressure at lower tank levels to feed your heater.
 
mpmillermg said:
Thanks for the quick reply Chris, I know that light you were talking about on the Fenway ignition control module. I have a different model of control module that does not have that light. I attached a picture of the model I have. You can see where there is the red blinking light is supposed to be is a chord that goes up to the panel. Mine will give you the error on the display and the only error I get is an ignition error.
Click to expand...
You have a later model “Connected” Master Temp heater with the 6 button control panel and diagnostics on the display instead of LEDs.

When was that heater installed?
 
I got it in
ajw22 said:
You have a later model “Connected” Master Temp heater with the 6 button control panel and diagnostics on the display instead of LEDs.

When was that heater installed?
Click to expand...
2021 is when it was installed. Yes I don’t have the LED lights on the back of the panel like some models. you can see the display in my video. I just have one light that blinks when it’s trying to heat and stays steady when it’s lit. If I get any errors they come on the screen
 
ajw22 said:
Just fill the tank.

A liquid propane tank takes thermodynamics to change it to gas and develop gas pressure. You cannot simply turn the pressure up.

The tank needs to be full enough to absorb heat fast enough from the air or ground (if it's buried) to boil the liquid propane in the tank to a gas. In the warmer months this is rarely ever an issue unless a tank is grossly undersized.

You have issues with your LP tank sizing or installation not creating enough gas pressure at lower tank levels to feed your heater.
Click to expand...
Thanks for the info, I think my tank should be plenty big enough. It ran fine last year and the year before that. My tank is not buried. I am going to have them come fill it.

What I don’t get is I measured the gas pressure coming into the gas valve on a anolog manometer and it measured at 10in/wc but when the heater starts up and fires it drops to 4in/wc. Wouldn’t that be something wrong with the gas valve if the pressure coming in is at 10in of WC? Some threads I watched said 10 inches of water column is ideal.
 
mpmillermg said:
Some threads I watched said 10 inches of water column is ideal.
Click to expand...
Sure, if you get 10 inches when the heater is operating.

full
 
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If you have liquid in the tank the vapor pressure is about 100 psi. So if you have any liquid that's the pressure in the tank give or take a few other minor affects. I see what Allen is talking about. When there's no flow your gas pressure is extremely low. When the blower lights your pressure drops like a rock to zero. Should be steady and much closer to 10" Looks like it pressures up the line with 4 in pressure then when the burner lights the gas only runs for a short time as all the gas is quickly consumed and the pressure drops to zero. There are a couple things that can cause this:
  • You're out of gas and your gauge is level gauge is incorrect. An easy way to check this is to add some gas so you know you have liquid in the tank (I think that's what Allen is saying).
  • If you do have 40% level in the tank then the likely problem is:
    • You've got an obstruction in the line - could be a valve that somebody partially closed also.
    • Your regulator is stuck and not providing enough flow.
If your flame lights and runs that long it's not usually the flame detection issue that can be very difficult to fix. There are other ways to confirm the actual level in the tank but adding some propane that you'll need sooner or later is a pretty easy way to do that. That's where I'd go next. One thing I learned about pool heater problems is similar to my sailing days. "If you don't know what the problem is try the easy stuff first."

I hope this is helpful.

Chris

1746416988317.png
 
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You can check at the inlet and at the manifold.

Do it both ways and show where you are connecting the test tubes.

The Manifold test needs to use both ports.
1746455959576.png

1746455968019.png




_____________________________________________________________
The inlet test only uses the inlet port.

1746456012320.png

1746456298597.png
 
JamesW said:
You can check at the inlet and at the manifold.

Do it both ways and show where you are connecting the test tubes.

The Manifold test needs to use both ports.
View attachment 643154

View attachment 643155




_____________________________________________________________
The inlet test only uses the inlet port.

View attachment 643156

View attachment 643157
Click to expand...
That's right, I remember getting educated on this point by @swamprat69 with my old Jandy. Still had negative pressure controller. I couldn't tell what he was measuring but thought it was supply pressure. Maybe not.

Chris
 
The gas line feeds into the suction side of the blower and this causes the pressure to be negative.

The vent line is also negative since it is also tapped into the blower suction side.

Before the gas valve opens, the vent has higher pressure and you get a positive reading since the vent is less negative than the gas line.

However, this is not gas pressure; it is only the vacuum created by the blower at two points and you get the difference.

When the gas valve opens, the pressure goes negative since the gas line is now higher pressure than the vent line.

It is confusing with all of the negative values.

For the inlet test, the pressure should be between 4" and 14" with the gas valve off or on and the pressure should drop about 0.5" w.c from off to on.

You only use the + port on the manometer and the - port is open to the air.
 
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1746460086255.png

The zero value is correct before the blower starts.

The 4.77" w.c is the blower vacuum at the vent and not gas pressure.

When the gas valve opens, the pressure does drop, which is correct, but it does not drop to -0.2, which indicates a lack of gas pressure.

Check the inlet gas pressure static and dynamic.

If it is good, you can increase the gas pressure.

The issue looks like a lack of Flame rectification, which could be a bad ignitor or maybe low gas pressure.

Check the ignitor resistance.

Check for 120 volts to the ignitor.

Check current going to the ignitor (About 3.5 to 4 amps AC).

Check Flame Current.

Heater Flame Sensing - Further Reading

www.troublefreepool.com www.troublefreepool.com
 
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All gas valves have an adjustment screw.

To increase, turn it clockwise with the heater running and manometer attached.

Turn it 90 degrees and read the manometer until you’ve reached the proper pressure.

This adjustment screw should not be tightened or loosened completely (bottomed out).

You need to increase the pressure, which is going to be more negative, which is confusing.

However, only do this if the inlet pressure is correct.

If the inlet pressure is too low, address that first.
 
You can perform some diagnostics on it to see if it is heating, examine it visually, check its resistance, which should be 60 ohms +/- 20 ohms.

Check that 120V AC is going to the igniter when the heater starts.

A new igniter resistance is 40 to 80 ohms.

The igniter is about 450 watts, which is about 3.75 amps at 120 volts.

1746462750747.png
 
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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.
 

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