Master Temp 400 cuts off after 30 seconds of heating

[bobbywebster22]

As my title says my pentair master temp 400 runs for about 30 seconds then cuts off with a service heater light. I have been attempting to trouble shoot for days but haven’t figured out the issue. There is no error light on the bottom of the board. I have replaced the thermal regulator twice. I have replaced the HLS and also took apart the inlet manifold and replaced the bypass valve even though it looked to be in good condition. I also replaced all o rings. There are also no flashing lights on the Fenwal.

At this point I think it might be a gas issue but I’m not 100% sure and I didn’t even know how to approach that.

 

[bobbywebster22]

As my title says my pentair master temp 400 runs for about 30 seconds then cuts off with a service heater light. I have been attempting to trouble shoot for days but haven’t figured out the issue. There is no error light on the bottom of the board. I have replaced the thermal regulator twice. I have replaced the HLS and also took apart the inlet manifold and replaced the bypass valve even though it looked to be in good condition. I also replaced all o rings. There are also no flashing lights on the Fenwal.

At this point I think it might be a gas issue but I’m not 100% sure and I didn’t even know how to approach that.

Also to add the heater does not attempt to refire, it just runs for 30 seconds or so, then the light comes on and the system idles.

 

[generessler]

As my title says my pentair master temp 400 runs for about 30 seconds then cuts off with a service heater light.

See this, especially the section on Heater Flame Sensing:

Pentair MasterTemp Heaters - Further Reading

www.troublefreepool.com

I went through something similar. As this doc explains, a likely cause is the Fenwal gas regulator flame sensor. You need to look at the LED on that device and count flashes to confirm. It's _not_ on the control board with all the other error indicators. A possible fix is to add a simple ground wire. In my case things started working again after I slightly tightened all the hardware in that area. The issue is that the valve turns itself off if it doesn't sense a flame. And that flame-sensing circuit is easily fooled by extra resistance between the igniter housing and true ground.

 

[bobbywebster22]

See this, especially the section on Heater Flame Sensing:

Pentair MasterTemp Heaters - Further Reading

www.troublefreepool.com

I went through something similar. As this doc explains, a likely cause is the Fenwal gas regulator flame sensor. You need to look at the LED on that device and count flashes to confirm. It's _not_ on the control board with all the other error indicators. A possible fix is to add a simple ground wire. In my case things started working again after I slightly tightened all the hardware in that area. The issue is that the valve turns itself off if it doesn't sense a flame. And that flame-sensing circuit is easily fooled by extra resistance between the igniter housing and true ground.

I appreciate the input! I did look at the fenwal unit after the service heater light would come on but I didn’t see any indicator lights flashing.

 

[setsailsoon]

Can you please post a photo of the unit control pad? Is there an error code? How old is this unit?

 

[ajw22]

You need to check gas pressures using a manometer.

Post pictures of the heater. Especially showing the gas line into the heater.

What is the CFM of your house gas meter? Post pictures of your gas meter and data plates on it.

My guess is you have a gas pressure problem or a Heater Flame Sensing - Further Reading problem.

Neither of them throw any error codes.

 

[setsailsoon]

Picking up on Allen's comment. Flame sensing problems are very likely to cause flashing light on the Fenwal. I would revert to my old sailing add age "Check the easy stuff first". Wouldn't be the first time somebody found a gas valve had been inadvertently partially closed or the supply pipe had corroded and caused a leak that reduced gas flow.

 

[ajw22]

How old is the heater?

How much corrosion is in the heater?

Is the heater controlled by any automation?

Does the heater have a 5 button or 6 button keypad?

Confirm you have removed the top and turned the board over to observe the diagnostic LEDs when the heater starts and shuts down?

Pentair MasterTemp Heaters - Further Reading

www.troublefreepool.com

The following are the LEDs:

1. .....PS (Pressure Switch)
2. .....HLS (High Limit Switch)
3. .....SFS (Stack Flue Sensor)
4. .....AFS (Air Flow Switch)
5. .....AGS (Automatic Gas Shutoff).
6. .....Service System
7. .....Thermistor
8. .....Heating
9. .....Pool On
10. ...Spa On
11. ...Service Heater.