I have a Pentair Matertemp heater. The problem is the heater is sensing a higher temp than the actual water temp is. I have replaced the thermister 2 times and still have the same issue. When I try to heat my hot tub I can only get the heat up to about 98 because the heater thinks it is 104 and will not heat anymore. The remote says it's only 98, and I have checked the temp of the water with a laser temp and it is only 98. So I can't heat the hot tub to around 100 or 101 like I prefer. Any insight into this will be greatly appreciated.
Pool Heater Issue
- Thread starter summron
- Start date
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- Tags
- heater problem
- Jul 21, 2013
- 54,789
- Pool Size
- 35000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Pentair Intellichlor IC-60
My heater just started doing the same thing. Heats fine to about 100 degrees. Aqualink shows a water temperature of 99-100 while the heater control panel shows a water temperature of 101-102. Heat cycles on and off continuously once it gets to that point.
My heater was installed in 2015 and worked flawlessly heating the spa to 102 until now. Aqualink and heater temperatures used to agree.
I just replaced the thermal regulator and bypass valve thinking it would be one of those. But they both looked good when removed. I now suspect it is the PCBA control board but I am going to hold off on replacing that for a while. I want to see if the new PCBA board with the RS-485 interface becomes available.
I share your enjoyment of a 102 degree spa. If my heater heats the pool fine and spa to 100 for this year I may let it go for another year.
When I get a chance I am going to examine my PCBA board closely along with the wiring especially to the thermistor.
@JamesW any insights into this problem we share?
My heater was installed in 2015 and worked flawlessly heating the spa to 102 until now. Aqualink and heater temperatures used to agree.
I just replaced the thermal regulator and bypass valve thinking it would be one of those. But they both looked good when removed. I now suspect it is the PCBA control board but I am going to hold off on replacing that for a while. I want to see if the new PCBA board with the RS-485 interface becomes available.
I share your enjoyment of a 102 degree spa. If my heater heats the pool fine and spa to 100 for this year I may let it go for another year.
When I get a chance I am going to examine my PCBA board closely along with the wiring especially to the thermistor.
@JamesW any insights into this problem we share?
Get a 10k ohm resistor to see what that reads by connecting it to where the thermistor connects.
Note: DO NOT run the heater like this. This is a test to see if the heater board is reading the resistance correctly.
Verify the resistor is 10k ohms with a good multimeter.
It should read 77 degrees on the display.
If it reads 77 degrees, the board is probably ok.
Check the board reading and then disconnect the thermistor wires from the board and check the resistance to see if the resistance converts to the same temperature.
Note: DO NOT run the heater like this. This is a test to see if the heater board is reading the resistance correctly.
Verify the resistor is 10k ohms with a good multimeter.
It should read 77 degrees on the display.
If it reads 77 degrees, the board is probably ok.
Check the board reading and then disconnect the thermistor wires from the board and check the resistance to see if the resistance converts to the same temperature.
Last edited:
- Jul 21, 2013
- 54,789
- Pool Size
- 35000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Pentair Intellichlor IC-60
Well my problem looks like it is the thermistor.
The problem got worse as my pool would not heat to 80F. At around 78F the MasterTemp display would show 110, 111 or 112. The gas would cycle on and off no doubt due to the temperature over the 104F maximum. The heater would stay there cycling and clicking with the fan running and occasional puffs of heat and then stopping.
I rigged up a 10K resistor connected to two alligator clamps.
Then I used two nails stuck in the connector to clip the alligator clips to.
With the 10K resistor in place the temperature read 76F and was stable as I ran the spa up to 102 and let it cycle there.
I took some electrical tape and taped the alligator clips to the connector to be able to run the heater until I get a new thermistor. The temperature is controlled by my Aqualink.
I buttoned up that side and now have the heater working for this weekend.
The problem got worse as my pool would not heat to 80F. At around 78F the MasterTemp display would show 110, 111 or 112. The gas would cycle on and off no doubt due to the temperature over the 104F maximum. The heater would stay there cycling and clicking with the fan running and occasional puffs of heat and then stopping.
I rigged up a 10K resistor connected to two alligator clamps.
Then I used two nails stuck in the connector to clip the alligator clips to.
With the 10K resistor in place the temperature read 76F and was stable as I ran the spa up to 102 and let it cycle there.
I took some electrical tape and taped the alligator clips to the connector to be able to run the heater until I get a new thermistor. The temperature is controlled by my Aqualink.
I buttoned up that side and now have the heater working for this weekend.
Most likely a bad thermistor.
However, I would be concerned that heated water was backing up into the inlet causing the water temperature to really be at 110.
You can get backup of heated water if the heat exchanger and the internal bypass are blocked for some reason.
In any case, do not operate a heater with any part bypassed.
If all parts are not functioning correctly, leave the heater off.
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You can connect the multimeter to the thermistor and read the resistance before the heater starts and as it starts. The resistance should match the water temperature without being jumpy.
Temp.....Ohms
73......... 11,029
74......... 10,761
75......... 10,500
76......... 10,246
77.......... 9,999
78......... 9,758
79......... 9,525
80......... 9,297
81......... 9,076
82........ 8,861
83........ 8,651
84........ 8,447
85.... ....8,249
86........ 8,056
87........ 7,867
88........ 7,684
89........ 7,506
90......... 7,333
91........7,164
92......... 6,999
93........ 6,839
94......... 6,683
95......... 6,530
96......... 6,382
97......... 6,238
98......... 6,097
99......... 5,960
100........ 5,827
101........ 5,697
102........ 5,570
103........ 5,446
104........ 5,326
Temp.....Ohms
73......... 11,029
74......... 10,761
75......... 10,500
76......... 10,246
77.......... 9,999
78......... 9,758
79......... 9,525
80......... 9,297
81......... 9,076
82........ 8,861
83........ 8,651
84........ 8,447
85.... ....8,249
86........ 8,056
87........ 7,867
88........ 7,684
89........ 7,506
90......... 7,333
91........7,164
92......... 6,999
93........ 6,839
94......... 6,683
95......... 6,530
96......... 6,382
97......... 6,238
98......... 6,097
99......... 5,960
100........ 5,827
101........ 5,697
102........ 5,570
103........ 5,446
104........ 5,326
- Jul 21, 2013
- 54,789
- Pool Size
- 35000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Pentair Intellichlor IC-60
The heat exchanger looks good.
And I replaced the bypass valve, thermal regulator, and O rings. So gave the heater a complete tune-up.
The heater ran so well with the 10K resistor in place I didn’t bother measuring the thermistor resistance as the water heated.
It feels like the water is heating up quicker now with the tune-up. Although the thermal regulator and bypass valve looked ok. I expected to find a broken bypass valve like shown in some YouTube videos.
And I replaced the bypass valve, thermal regulator, and O rings. So gave the heater a complete tune-up.
The heater ran so well with the 10K resistor in place I didn’t bother measuring the thermistor resistance as the water heated.
It feels like the water is heating up quicker now with the tune-up. Although the thermal regulator and bypass valve looked ok. I expected to find a broken bypass valve like shown in some YouTube videos.
Here is an update for me. I connected a multimeter to the thermistor and it is reading the correct temp which matches what my remote says, but the temp on the heater is incorrect.
For example the multimeter reading is 72, the remote says 72, but the heater is showing 81 degrees.
I took an old thermister and checked it with the multimeter and it was accurate. I then plugged it into the wires on the heater, but did not screw it into the manifold on the heater. I turned the spa on and the heater perfect up to 102 degrees and shut off, once the temp dropped it heater back up to 102. It worked great. The whole time the heater thought the temp was only 72 and never went up because it was plugged into a thermister that was not reading anything but the air temp. The remote controll the temp just fine.
This leads me to think that the control board may be bad. If anyone has some experience with this could you please confirm this thought process. Thank you!!
@JamesW Any thoughts on this?
For example the multimeter reading is 72, the remote says 72, but the heater is showing 81 degrees.
I took an old thermister and checked it with the multimeter and it was accurate. I then plugged it into the wires on the heater, but did not screw it into the manifold on the heater. I turned the spa on and the heater perfect up to 102 degrees and shut off, once the temp dropped it heater back up to 102. It worked great. The whole time the heater thought the temp was only 72 and never went up because it was plugged into a thermister that was not reading anything but the air temp. The remote controll the temp just fine.
This leads me to think that the control board may be bad. If anyone has some experience with this could you please confirm this thought process. Thank you!!
@JamesW Any thoughts on this?
Note: DO NOT run the heater like this. This is only a test to see if the heater board is reading the resistance correctly.
Get a 10k ohm resistor to see what that reads by removing the wires from the heater thermistor and connecting them to the resistor.
It should read 77 degrees on the display.
If it reads 77 degrees, the board is probably ok.
Note: DO NOT run the heater like this. This is only a test to see if the heater board is reading the resistance correctly.
Get a 10k ohm resistor to see what that reads by removing the wires from the heater thermistor and connecting them to the resistor.
It should read 77 degrees on the display.
If it reads 77 degrees, the board is probably ok.
Note: DO NOT run the heater like this. This is only a test to see if the heater board is reading the resistance correctly.
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This shows the wires connected to the resistor instead of being connected to the thermistor.
With it like that, the heater display should be 77 degrees.
If the heater display is 77 degrees, the board is probably OK and the problem is probably the thermistor.
If the heater display is not 77 degrees (+/- 1 degree), then the board is probably bad.
Note: Do not operate the heater like this. It is only a test.
- Jul 21, 2013
- 54,789
- Pool Size
- 35000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Pentair Intellichlor IC-60
Sounds to me like your board is fine if it took your spa up to 102 with the old thermistor reading a constant 72.
You should do the 10K resistor test.
I know you said you tried two new thermistors. I would try one more.
James mentioned about heated water backing up into the inlet. I opened up my manifold and replaced the thermal regulator and bypass valve. If your temperature still does not read correctly I think it is time to open up the manifold and see what is going on there.
This is a test to see if the heater board is reading the resistance correctly.
Do not run the heater with the resistor in place of the thermistor.
Do not run the heater with the resistor in place of the thermistor.