Pentair MasterTemp 250 shuts down after 3 tries- No error codes

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rchadha

Silver Supporter
May 2, 2022
32
Pittsburgh
Pool Size
19000
Surface
Vinyl
Chlorine
Liquid Chlorine
Hi all,
Pool season is about to be over here in western PA and my pool heater has started giving me some trouble.
For reference, I have a Pentair MasterTemp 250. Installed in 2012. We bought the house in 2021 and the heater worked fine last 2 years.
When I turn the heater on, it goes through its regular on sequence, the gas is ignited (I hear the whoosh sound), and hot air starts coming out of the exhaust. But within 5s, I hear a relay click and the heating turns off (no more hot air from the exhaust). The heater tries this sequence again after 15ish seconds, and the same results. It runs for 5s and then turns off. After 3 attempts the service heater LED is on and it stops any further heating attempts.

I have looked behind the front panel, and I don't see any error code LEDs on. I have also checked the following sensors:

1. Water pressure switch: Working, I see a short on the multimeter, when the flow rate is sufficient. For now, I am running my VSP on max speed while I debug this issue, so I don't think the flow rate is an issue.

2. HLS: Working, I see a short on the multimeter.

3. AGS: Working, I see a short on the multimeter

4. Thermistor: Measured the resistance and it seems to match the water temperature

5. Air flow switch: Working, checked with a multimeter

6. SFS: Again, I can see the SF temperature go up when the heater is running for 5s, it goes up to 125. But since the heater turns off, after 5s, it stops rising.

7. Thermal regulator: I saw on some threads that this can be caused by the thermal regulator not moving. I checked the regulator. Initially, I suspected it and replaced it (it was a little corroded), but the issue persists even after regulator replacement.

At this point, I am not sure what else I can do. It appears that the heater tries to fire (indeed starts heating), but some sensor tells it that there's a fault and it turns itself off. Where this could be, I am not sure.
Any suggestions and guidance for the next steps to troubleshoot will be really appreciated. Thanks so much!
 
rchadha said:
Hi all,
Pool season is about to be over here in western PA and my pool heater has started giving me some trouble.
For reference, I have a Pentair MasterTemp 250. Installed in 2012. We bought the house in 2021 and the heater worked fine last 2 years.
When I turn the heater on, it goes through its regular on sequence, the gas is ignited (I hear the whoosh sound), and hot air starts coming out of the exhaust. But within 5s, I hear a relay click and the heating turns off (no more hot air from the exhaust). The heater tries this sequence again after 15ish seconds, and the same results. It runs for 5s and then turns off. After 3 attempts the service heater LED is on and it stops any further heating attempts.

I have looked behind the front panel, and I don't see any error code LEDs on. I have also checked the following sensors:

1. Water pressure switch: Working, I see a short on the multimeter, when the flow rate is sufficient. For now, I am running my VSP on max speed while I debug this issue, so I don't think the flow rate is an issue.

2. HLS: Working, I see a short on the multimeter.

3. AGS: Working, I see a short on the multimeter

4. Thermistor: Measured the resistance and it seems to match the water temperature

5. Air flow switch: Working, checked with a multimeter

6. SFS: Again, I can see the SF temperature go up when the heater is running for 5s, it goes up to 125. But since the heater turns off, after 5s, it stops rising.

7. Thermal regulator: I saw on some threads that this can be caused by the thermal regulator not moving. I checked the regulator. Initially, I suspected it and replaced it (it was a little corroded), but the issue persists even after regulator replacement.

At this point, I am not sure what else I can do. It appears that the heater tries to fire (indeed starts heating), but some sensor tells it that there's a fault and it turns itself off. Where this could be, I am not sure.
Any suggestions and guidance for the next steps to troubleshoot will be really appreciated. Thanks so much!
Click to expand...
You will have to look on the back of the control board , while the heater is trying to light, for a small LED that will be next to the description of the sensor that tripped the "service heater" code. That does not mean that sensor is bad, but that it is doing its job and give an area to start looking.
 

Fenwal LED Light.​

The LED will flash on for 1/4 second, then off for 1/4 second during a fault condition. The pause between fault codes is 3 seconds. The LED light on the Fenwal box can indicate the following problems:
  • Steady on - Internal Control Failure
  • One flash - Air Flow fault
  • Two flashes indicates flame no call for heat, then the Fenwal is detecting a flame current when it shouldn't be
  • Three flashes indicates no flame current being sensed and ignition locked out

Testing the Flame Sense Circuit.​

The Fenwal has two test points for flame current FC+ and FC-.

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

The best way to measure the flame sense current is with a true RMS meter.

Measure the current with a good true RMS meter that can measure dc current in the microamp range.

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. Voltage is an indirect indication but easier to do with typical DIY equipment.

But it's still very difficult to measure unless you make up some pin wires to clip your voltmeter to.

Or you can order some insulated micro clips for the test.

The reading should be 3-8 volts and this corresponds to the millionth's of an amp signal your flame sense signal should reading.

When not operating, the flame current should read 0 volts dc and 0 microamps dc. DC amps and voltage should be zero when there is no flame.

When there is a flame, there are ions in the flame that can carry current from the flame sensor to the burner and then through the ground back to the Fenwal.

The current mostly goes in one direction, so it's "rectified" from ac to dc.

This is called "flame rectification" and it's how the Fenwal verifies that the burners actually light when the gas valve opens.
 
1poolman1 said:
You will have to look on the back of the control board , while the heater is trying to light, for a small LED that will be next to the description of the sensor that tripped the "service heater" code. That does not mean that sensor is bad, but that it is doing its job and give an area to start looking.
Click to expand...
Have you checked out the pilot igniter? It could be dirty, covered by spider webs, or simply defective
 
Thank you @1poolman1 @JamesW @oldprophet for replying to this thread.

I did not see any fault LEDs on the control board, so I started investigating the Flame Sense circuit.
When the issue occurs, the Fenwal shows ignition lockout (3 LED blinks).

I am measuring the resistance of the igniter as 91 ohms. So probably it's wearing out. But it still ignites. Perhaps the higher impedance is causing an error in the flame sense measurement?

After opening the Fenwal box, I saw 2 things:
1. The voltage between FC+/- never goes above 0.4V. I don't have a True RMS uAmmeter at the moment.
2. Lot of corrosion around the chassis GND inside the Fenwal box (& lots of mouse poop).

I feel that the combination of the higher resistance of the igniter and increased resistance at GND junction is causing the flame sense current to be very low, which is then causing the Fenwal to lock out. What do you think?

Here's what I am thinking I will try (in the following order):

1. Clean the GND juction, with sand paper and try to get a very good GND with the chassis. Any suggestions on how to clean it super well?
2. Replace the igniter (will need a couple of days to arrive).
3. Verify the flame sense current with a true RMS ammeter (will need a couple of days).

Anything else I should try? Thanks again and I appreciate all your help!





IMG_0203.jpg
 
Thanks @JamesW
Quick update. I cleaned the GNDs with sand paper and rubbing alcohol, and that fixed the issue. So the GND was the culprit.
I still need to replace the ring connectors as they broke while I was removing them.
It’s surprising how corrosive mouse pee can be😝
The igniter will be next on the things to change out.
Thanks for all the help!
 
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JamesW said:
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@JamesW
Re-starting this thread.. My heater was not starting (3 tries and then a service heater error). I cleaned the GND in the Fenwal box and it worked once, but this has been a recurring problem. I haven't had a chance to update this thread, but the heater still has the same issue. Cleaning the GND inside the Fenwal box didn't really solve it.
Every time I turn the heater on, the ignitor ignites the gas and then in a few seconds, the gas is shut off by a relay. This happens 3 times, after which the heater quits trying and then gives the service heater error on the control panel. On the Fenwal box, the red LED blinks 3 times, indicating ignition lockout.
The current measured in the Fenwal is less than 1uA. So I am suspecting that's probably why the gas gets turned off by Fenwal.
However, I have replaced the ignitor, cleaned the GND around each terminal, and even added the extra GND kit that Pentair provides, but it still hasn't fixed the issue.
To get the heater to work, I have to almost always remove the ignitor and put it back in, reconnect it, and then it turns back on. I don't understand what could be happening by removing and putting the ignitor back in, that makes it work.
When this happens the Fenwal current is still less than 2uA, but the heater is able to sustain the flame and continues to run.

I am not sure what is really wrong at this point. Any suggestions on what I can try next? Do you think that the Fenwal controller is bad?
 
This pic show you have a lot of corrosion in the heater. The corrosion is disrupting the ground path used for the flame sensing. that is a weakness of the Pentair design. You can’t let this type of corrosion spread and once it does it is difficult to repair.

When you mess with the igniter you create a good enough connection for the heater to ignite a few times and then the corrosion returns to the metals in the area.

The corrosion in the heater is probably terminal and it needs to be replaced. I would stop throwing parts and money into a corroded chassis.

img_0203-jpg.525239
 
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