MasterTemp 400 Service Heater Light On Heater Cycling

[-Ed]

Hi, my 2007 MasterTemp 400 has worked fine all summer. My cover broke in the closed position and the pool wasn't used for 4 weeks but I kept the pump running with the heater off. When the cover was repaired I turned the heater on and it brought the pool up from 62º to 79º and then shut down before reaching my setting of 86º and the Red Service Heater Light goes on. Now I cannot keep it running long enough to maintain any setting.

I have been troubleshooting the system: June of this year I replaced the Gas Control Valve when the old one died. This solved that problem. The heater continued to work flawlessly until Labor day when I turned if off because the cover was stuck in the closed position. So here we are 2 weeks into October and the heater has begun cycling on and off a couple times then goes into Service Heater Mode, the red light on and the fan stops running.

The heater fires up and runs a few minutes but then shuts down. It retries and then shuts down again. The third time the Service Heater Light comes on and the heater quits working.

After reading about flow issues, I replaced the cartridge filter, and cleaned the skimmer and the pump basket strainer with no results. I also checked that all valves were in the Full On position.

There are no error codes or lights on the back of the circuit board.

I have now replaced the High Limit Switch and the Automatic Gas Shut off switch. Again, with no results.

I pulled the thermostat and replaced it for good measure. The old one wasn't looking great and didn't seem to be performing well.

Could the Water Pressure Switch be causing the heater to cycle?

I guess I'll replace the Water Pressure Switch? It has a knurled knob that is all the way to the clockwise stop. This is my last straw. I'm not sure I know what to do next? If it were the Stack Sensor I would have an error code. I worked on that one last summer.

 

[ajw22]

Stop throwing parts at it.

It is not the Water Pressure switch.

It may be the thermal regulator or the bypass valve.

Did you turn the main board over and watch the diagnostic LEDs when the heater shuts down prematurely?

Pentair MasterTemp Heaters - Further Reading

www.troublefreepool.com

 

[JamesW]

Check the flame current.

Check the Fenwal for three flashes of the LED.

Heater Flame Sensing - Further Reading

www.troublefreepool.com

 

[JamesW]

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.

If you try to check this be very careful since you can easily short the 24 vac circuit which can blow the transformer before the 2 amp fuse blows.

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.

 

[JamesW]

Can you show pictures of everything?

 

[1poolman1]

Hi, my 2007 MasterTemp 400 has worked fine all summer. My cover broke in the closed position and the pool wasn't used for 4 weeks but I kept the pump running with the heater off. When the cover was repaired I turned the heater on and it brought the pool up from 62º to 79º and then shut down before reaching my setting of 86º and the Red Service Heater Light goes on. Now I cannot keep it running long enough to maintain any setting.

I have been troubleshooting the system: June of this year I replaced the Gas Control Valve when the old one died. This solved that problem. The heater continued to work flawlessly until Labor day when I turned if off because the cover was stuck in the closed position. So here we are 2 weeks into October and the heater has begun cycling on and off a couple times then goes into Service Heater Mode, the red light on and the fan stops running.

The heater fires up and runs a few minutes but then shuts down. It retries and then shuts down again. The third time the Service Heater Light comes on and the heater quits working.

After reading about flow issues, I replaced the cartridge filter, and cleaned the skimmer and the pump basket strainer with no results. I also checked that all valves were in the Full On position.

There are no error codes or lights on the back of the circuit board.

I have now replaced the High Limit Switch and the Automatic Gas Shut off switch. Again, with no results.

I pulled the thermostat and replaced it for good measure. The old one wasn't looking great and didn't seem to be performing well.

Could the Water Pressure Switch be causing the heater to cycle?

I guess I'll replace the Water Pressure Switch? It has a knurled knob that is all the way to the clockwise stop. This is my last straw. I'm not sure I know what to do next? If it were the Stack Sensor I would have an error code. I worked on that one last summer.

Running the adjustment knob all the way clockwise has increased the amount of pressure needed to close the switch. Put it back where it was or, since it has been disturbed and isn't expensive, go ahead and replace it. Adjusting a pressure switch is only needed when the equipment is far below pool level. Under normal conditions a working pressure switch will not cause cycling. You changed that.

As has been said, you need to check the diagnostic LEDs on the back of the ciruit board.

 

[JamesW]

There are no error codes or lights on the back of the circuit board.

The third time the Service Heater Light comes on and the heater quits working.

This points to a flame sensing issue.

Either the flame is weak or the flame is not being sensed correctly.

Check the flame current.

Check the gas pressure static and dynamic.

Check for water in the combustion chamber by removing a bottom manifold bolt.

 

[JamesW]

If the pressure switch was the problem, it would say "Service System".

The problem reported is "Service Heater".

Service Heater with no error codes or lights is usually a flame sensing issue, which can be confirmed by checking the Fenwal for the LED to flash 3 times.

Going into lockout after three times also points to a flame sensing issue.




Why was the pressure switch adjusted?

Is it working correctly?

Is the equipment above or below the pool?

 

[-Ed]

I have observed the red LED on the Fenwall box when firing up the heater. The fan comes on and the flame is lit. Then the heater shuts down and the red LED blinks three times. I measured the DCVoltage across the FC terminals and found it to fluctuate around 1.75 VDC. I installed the additional ground wire as described. There are no diagnostic LED's lighted on the underside of the touch panel. The Pool On light and the Service Heater lights are on. I have replaced the Thermal Regulator.

Note: The pressure switch adjustment is how I found it, the reason I looked for it was because of a note in the troubleshooting manual, that page is attached with photos. Also, about two weeks ago the igniter went bad and was replaced. The pool heated from 62º to 79º after the igniter was replaced. It was at 79º that the heater stopped working normally and began to cycle. At this time it is no longer cycling. It comes on for a puff and then goes into 'Service Heater' mode.

 

[ajw22]

I see a lot of corrosion on the burner can, around the electrical box, and other areas. All of that corrosion affects the paths for the flame sensing current.

1.75 volts is not enough. As was said above the reading should be 3-8 volts and this corresponds to the millionth's of an amp signal your flame sense signal should reading.

In the various work you recently did in the heater you probably disturbed the electrical ground path that was working. I would work on cleaning up corrosion under all the screws and metal connections.

Show us where you connected the new ground wire.

Heater Flame Sensing - Further Reading

www.troublefreepool.com

@swamprat69

 

[JamesW]

Remove one of the bottom bolts to see if water comes out.

If water comes out, there is water in the combustion chamber.

 

[-Ed]

I installed the ground wire between the flange and one of the flange screws as pictured in the first two photos with no change. Then I started over from scratch and installed it between the flange and a grounded screw in the box that contains the Fenwall as shown in the third and fourth photos.

Is there a reset button that I should be pressing after this goes into the three blink mode?

 

[JamesW]

That's a lot of corrosion.

Is the combustion chamber blowing out hot exhaust anywhere?

It looks like the combustion chamber is no longer solid enough to trust.

At this point, I would probably look into replacing the heater.

Verify the gas pressure is good before firing (static) and during firing (dynamic).

 

[JamesW]

 

[-Ed]

Remove one of the bottom bolts to see if water comes out.

If water comes out, there is water in the combustion chamber.

View attachment 458998

I removed that bolt and it's dry and no water came out.

 

[JamesW]

It looks like the tub is no longer airtight.

Has the corrosion cause the tub to leak exhaust?

 

[ajw22]

Is there a reset button that I should be pressing after this goes into the three blink mode?

The reset button is a power cycle OFF then ON.

 

[-Ed]

That's a lot of corrosion.

Is the combustion chamber blowing out hot exhaust anywhere?

It looks like the combustion chamber is no longer solid enough to trust.

At this point, I would probably look into replacing the heater.

Verify the gas pressure is good before firing (static) and during firing (dynamic).

I haven't detected hot air inside of the heater cabinet and I've been all over it looking for issues.

 

[-Ed]

The tub is dry as a bone, no water came out when I removed the bolt. Is it possible that when I installed the igniter the gasket didn't seat properly? It ran for two days before this problem arose. I checked out the two videos of the heater core replacement. This components appear in much better shape than that one, and I would surely replace the entire unit before doing a core exchange.

Is there a flame sensor?

 

[JamesW]

It seems to be a flame current issue, which can be due to a weak flame or a defect in the flame sensing circuit.

The corrosion has probably interfered with the flame circuit path.

It looks like the corrosion is bad enough that getting a good flame current path will be difficult.

A weak flame can be due to low gas pressure due to a gas line problem or maybe a defective gas valve.

You can check the gas pressure to see if it is in range.

A poor flame can also be caused by other issues.

Is the combustion chamber corroded completely through anywhere?