Mastertemp 400 Wrong Temperature Readings

[mflores83]

I have a Mastertemp 400 pool and spa heater. It does 1 of 2 things currently:

1) Reads in the inlet temperature in the 90s, water is likely in the 70s. Heater will kick on and heat for about a minute before the temperature rises to 126 rapidly and kicks off the heater

2) When turned on the water temperature shows above 104 so it will not kick the heater on

I ordered a thermostat, a high limit switch, and thermal regulator. All independently did not resolve the issue, same exact things would happen. My parents have the same heater and it is working fine, so I tested the new thermostat, works as it should. Tested my control panel on their heater, works as it should. Tested my wires that go from the thermostat to the control panel on their heater and it works as it should.

Does anything else read the temperature from the incoming water? Am I missing something? I am stumped.

Thanks in advance,

Matt

 

[ajw22]

Welcome to TFP.

I don't know what the thermostat is. You mean the temperature thermistor?

Is your heater connected to an automation panel?

Check the bypass valve in the manifold.

Pentair MasterTemp Heaters - Further Reading

www.troublefreepool.com

 

[1poolman1]

Thermostat? Do you mean thermister? That is what senses inlet temperature in a Master Temp heater. High limit switches are just that. They are mechanical and open at a preset temperature, basically on/off. Thermal regulator adjusts waterflow through the heat exchanger for optimum heating. A quick rise like you see can be caused by a bad/broken internal bypass assembly. Bad/erroneous inlet temp should be a bad thermister

 

[mflores83]

Yes, it was the thermistor I was referring to that I ordered and replaced. I will order the bypass valve and have it ready to replace should it be broken when I open it up.


Thanks!

 

[ajw22]

Are you sure you got a genuine Pentair thermistor?

The lower priced “Pentair type” thermistor are not from Pentair and some people have had problems with them.

 

[mflores83]

Yep, it is a genuine part and I know it is good since the new part I ordered works in my parents heater.

 

[ajw22]

Yes, it was the thermistor I was referring to that I ordered and replaced. I will order the bypass valve and have it ready to replace should it be broken when I open it up.


Thanks!

You should also get the manifold O ring kit and replace them while you have it open.

 

[mflores83]

Got the part and had time to take off the manifold. Bypass valve was intact and looked fine. It was a little harder to depress as opposed to the new one I ordered. Figured I have it apart, might as well replace it. Put it all back together, fired it up and I have the same issue. Any other parts that make sense?

Have called a couple pros, but none have called me back.

Side note, I am seriously thinking about adding automation. I know you need to add a temperature sensor that hooks into the automation panel. Does that completely bypass the heater itself reading the water temp? Or is that solely to show the temp on the control panel and remote?

 

[ajw22]

Which exact problems are you still having?

For a test replace the thermistor with a 10K resistor.

If the heater starts and reads 76F then you have a problem with the new thermistor.

If the heater does not read 76F steadily then you have a problem with the board or wiring to the thermistor.

Pentair MasterTemp Heaters - Further Reading

www.troublefreepool.com

Temperature Sensors - Further Reading

www.troublefreepool.com

 

[ajw22]

I know you need to add a temperature sensor that hooks into the automation panel. Does that completely bypass the heater itself reading the water temp? Or is that solely to show the temp on the control panel and remote?

No, the operate independently.

 

[mflores83]

Which exact problems are you still having?

For a test replace the thermistor with a 10K resistor.

If the heater starts and reads 76F then you have a problem with the new thermistor.

If the heater does not read 76F steadily then you have a problem with the board or wiring to the thermistor.

Pentair MasterTemp Heaters - Further Reading

www.troublefreepool.com

Temperature Sensors - Further Reading

www.troublefreepool.com

Thanks. I will order a 10k resistor. Wiring, thermistor and board have all been check on a know working heater and all worked find. The problem I am having is that it will show the temp rapidly increasing and shut off or read above 104 so it never turns on.

 

[mflores83]

Which exact problems are you still having?

For a test replace the thermistor with a 10K resistor.

If the heater starts and reads 76F then you have a problem with the new thermistor.

If the heater does not read 76F steadily then you have a problem with the board or wiring to the thermistor.

Pentair MasterTemp Heaters - Further Reading

www.troublefreepool.com

Temperature Sensors - Further Reading

www.troublefreepool.com

So I used the 10k resistor. Temp read 76 degrees and the heater kicked on. Was heating for a minute or two before the service heater light went on and the back showed this. So I ordered a new thermistor and ags valve from Pentair’s store on Amazon. Unless I am reading the LEDs wrong, I believe those two things should resolve it. Thanks again.

Matt

 

[1poolman1]

AGS errors are usually caused by a bad internal bypass. Too much water is bypassing the heat exchanger internally. What water that is going through is coming out too hot and tripping the AGS switch in the manifold.

 

[ajw22]

Did you order a new AGS sensor or gas valve?

From Pentair MasterTemp Heaters - Further Reading

You can test your AGS sensor..

• Remove the leads from the AGS sensor and connect them together. Temp only for the test.
• Then, check the continuity of the sensor. It should be closed.
• Start the heater. If the sensor opens, immediately turn off the heater.
• If the sensor opens, it might be a bad sensor or the water is overheating.
• To test the sensor, put it in hot water to see where it actually opens.
• If the sensor does not open and the heater shuts off with an AGS light, the board is bad.

 

[mflores83]

Did you order a new AGS sensor or gas valve?

From Pentair MasterTemp Heaters - Further Reading

You can test your AGS sensor..

• Remove the leads from the AGS sensor and connect them together. Temp only for the test.
• Then, check the continuity of the sensor. It should be closed.
• Start the heater. If the sensor opens, immediately turn off the heater.
• If the sensor opens, it might be a bad sensor or the water is overheating.
• To test the sensor, put it in hot water to see where it actually opens.
• If the sensor does not open and the heater shuts off with an AGS light, the board is bad.

I ordered this part in addition to another thermistor:

Pentair 42002-0025S 140F Automatic Gas Shutoff Switch​

The AGS switch read open, but the heater also thinks it is 120 degrees right now. I have no way of reading the water temp to see when it opens. AGS switch is set to come between the 2nd and 5th. Hopefully that resolves it.

 

[mflores83]

AGS errors are usually caused by a bad internal bypass. Too much water is bypassing the heat exchanger internally. What water that is going through is coming out too hot and tripping the AGS switch in the manifold.

Part #

77707-0001 ?​

I replaced that on Sunday. Though the original was all in one piece and spring seemed to function fine.

 

[mflores83]

If I were to take the AGS switch and the thermistor off of my parents heater (same model) and put in mine, can that damage either of those parts by running on my heater? Do not want to attempt it if can result in my parents heater having issues.

Thanks,

Matt

 

[JamesW]

Do you have an external bypass?

Can you show the whole system?

 

[mflores83]

No external bypass. I can take some pictures later.

 

[Poolbreh]

It sounds like you have a blocked downstream internally or externally. Causing the water in the exchanger to back up into the top of the manifold. That’s where your ags and thermistor are.