Mastertemp 250 5 button SFS Light - New thermal regulator and unsure how to proceed

[Garrettmueller]

Haven't ran the heater all summer. Unsure of the age but everything inside is very clean and all the rubber tubing and other components still look brand new. After trying it last week, it fired right up, and then after about 3 minutes it turned off and the service heater light came. I took the cover off and the SFS light is on. No other codes on the screen. I rebooted it and started it again watching the SFS temp and it quickly shot up to 480. The manual says to check the thermal regulator first. I pulled it and it looked somewhat corroded, it would not open under my kitchen sink hot water so purchased a new one. After installing the new thermal regulator I started the heater and it ran for about 10 minutes and then got the SFS code again.

I checked the resistance of the sensor while installed and got 3.138. Inside the house is 3.3-3.5. Played with it in cold water and hot water and am pretty convinced it works but please advise. Hot tap water decreases it to 1.1-1.2 and cold water from the refrigerator brings it up to 4 and then my meter shows the overload symbol (I believe). Tracks similar with this post. I have continuity between the wires at the sensor and the control board.

Not sure what to do next. The diagnostic guide from the manual has the next step from continuity - does it show E05 or E06 (no) and then from there, basic model has the next step as replace control board. Since I have the 5 button I'm not sure if I want to immediately upgrade to the new control board and screen if that isn't going to solve my problem.

In this thread, it is suggested to try running the heater with the thermal regulator removed and monitor stack temperatures. I have not done this but will do it and observe what happens as soon as I can. Also, Mknauss mentions that it is possible the thermal regulator is not in the hole it is supposed to sit in. I tried 3 or 4 times to get it in there properly, I could hear the ridge of it clicking on the plastic and I think falling into the hole. But will try again several more times after running the heater with it removed. It is certainly possible the new one is not installed properly.

Another thing I did is I ran the heater with the SFS sensor disconnected to see if it would throw a code. Surprisingly, it did not. It started up and worked for a few minutes before I decided to turn it off. During this time the stack temperature on my display read 40. I'm not sure if this is indicative of a failed control board. I don't know what it is supposed to read when you disconnect the sensor. Additionally, during all of these tests, I don't find the surface of the burner/furnace area and the exhaust or grate/piping to be all that hot. I can touch them with my hand for a few seconds while the heater is running and when it turns off for high SFS temps. Next is an IR thermometer to confirm but still really not sure.

Tried to do as much research before making a post as I could but not sure where to go other than a new control board according to the manual. Thanks.

 

[1poolman1]

Haven't ran the heater all summer. Unsure of the age but everything inside is very clean and all the rubber tubing and other components still look brand new. After trying it last week, it fired right up, and then after about 3 minutes it turned off and the service heater light came. I took the cover off and the SFS light is on. No other codes on the screen. I rebooted it and started it again watching the SFS temp and it quickly shot up to 480. The manual says to check the thermal regulator first. I pulled it and it looked somewhat corroded, it would not open under my kitchen sink hot water so purchased a new one. After installing the new thermal regulator I started the heater and it ran for about 10 minutes and then got the SFS code again.

I checked the resistance of the sensor while installed and got 3.138. Inside the house is 3.3-3.5. Played with it in cold water and hot water and am pretty convinced it works but please advise. Hot tap water decreases it to 1.1-1.2 and cold water from the refrigerator brings it up to 4 and then my meter shows the overload symbol (I believe). Tracks similar with this post. I have continuity between the wires at the sensor and the control board.

Not sure what to do next. The diagnostic guide from the manual has the next step from continuity - does it show E05 or E06 (no) and then from there, basic model has the next step as replace control board. Since I have the 5 button I'm not sure if I want to immediately upgrade to the new control board and screen if that isn't going to solve my problem.

In this thread, it is suggested to try running the heater with the thermal regulator removed and monitor stack temperatures. I have not done this but will do it and observe what happens as soon as I can. Also, Mknauss mentions that it is possible the thermal regulator is not in the hole it is supposed to sit in. I tried 3 or 4 times to get it in there properly, I could hear the ridge of it clicking on the plastic and I think falling into the hole. But will try again several more times after running the heater with it removed. It is certainly possible the new one is not installed properly.

Another thing I did is I ran the heater with the SFS sensor disconnected to see if it would throw a code. Surprisingly, it did not. It started up and worked for a few minutes before I decided to turn it off. During this time the stack temperature on my display read 40. I'm not sure if this is indicative of a failed control board. I don't know what it is supposed to read when you disconnect the sensor. Additionally, during all of these tests, I don't find the surface of the burner/furnace area and the exhaust or grate/piping to be all that hot. I can touch them with my hand for a few seconds while the heater is running and when it turns off for high SFS temps. Next is an IR thermometer to confirm but still really not sure.

Tried to do as much research before making a post as I could but not sure where to go other than a new control board according to the manual. Thanks.

Heater should not have started with the SFS disconnected. With no sensor, the display would be meaningless.
Those sensors go bad and are relatively inexpensive, unless you buy OEM ($100.00+. Pentair admits they've had issues with theirs). I have used the ones from Wholesale Sensors ($6.37 Amazon) and Optimum Pool Technologies (came in a kit, but $19.99 on Amazon). Worth a try and an easy repair.

 

[Garrettmueller]

Heater should not have started with the SFS disconnected. With no sensor, the display would be meaningless.
Those sensors go bad and are relatively inexpensive, unless you buy OEM ($100.00+. Pentair admits they've had issues with theirs). I have used the ones from Wholesale Sensors ($6.37 Amazon) and Optimum Pool Technologies (came in a kit, but $19.99 on Amazon). Worth a try and an easy repair.

That’s what I’m concerned with - the manual leads me to believe it’ll throw a code for open circuit when the sensor is disconnected. Either on startup or during operation. But the heater functioned fine for several minutes.

When holding down the spa button to see the SFS temp, it showed 40 degrees which makes me think that the logic on the control board is not reading the sensor properly. Do you know what a known good board is supposed to display on that SFS temp screen when the SFS is disconnected?

I saw both of those plus another listing on Amazon. I’ll order one of each and try them, and compare with my meter to the one I pulled.

 

[ajw22]

When holding down the spa button to see the SFS temp, it showed 40 degrees which makes me think that the logic on the control board is not reading the sensor properly.

That is not 40 degrees.

40 indicates the board is not getting a reading from the SFS.

My understanding is if you hold down the "pool on" button, it stays on 80, then flashes to 40, then back to 80, then the 80/40 reading and E05 indicate that the board is not getting a reading from the sensor.

 

[Garrettmueller]

My understanding is if you hold down the "pool on" button, it stays on 80, then flashes to 40, then back to 80, then the 80/40 reading and E05 indicate that the board is not getting a reading from the sensor.

I repeated this with the sensor unplugged and it still read 40 - it did not show 80 or the E05 code.

Wholesale Sensors ($6.37 Amazon)

I ordered one of these as well as another brand (Funmit) based on shipping times and it resolved the issue. I ran the heater for almost an hour today with the new sensor and no problems. Interesting that the sensor tests in range and appears to fluctuate with temperature but still causes an error during operation. I appreciate the guidance on just trying a new one.

 

[bradgray]

That is not 40 degrees.

40 indicates the board is not getting a reading from the SFS.

My understanding is if you hold down the "pool on" button, it stays on 80, then flashes to 40, then back to 80, then the 80/40 reading and E05 indicate that the board is not getting a reading from the sensor.

This is correct. It will show one or both when the SFS has failed or is absent.

While still failing, it can give you obviously incorrect readings or jump around, meaning the temp doesn't rise incrementally.

The temperature should rise very steadily. Not make huge leaps, and never go backward. You'll need to continually re-enter the temp readout a few times to keep a close eye to verify.

If you see it behave properly and then eventually reach 480, then it's measuring the exhaust properly and this is not your issue.

 

[Garrettmueller]

The temperature should rise very steadily. Not make huge leaps, and never go backward. You'll need to continually re-enter the temp readout a few times to keep a close eye to verify.

Before it would reach 300 almost immediately and then reach 480 and shutoff within 10-15 minutes, now it stays at 315 consistently while running.

 

[bradgray]

Before it would reach 300 almost immediately and then reach 480 and shutoff within 10-15 minutes, now it stays at 315 consistently while running.

It's normal for them to climb through 200s relatively fast. That's not necessarily unusual.

Was the climb to 480 incremental over that 10-15? Or rapid and then hold? Any bouncing or back and forth?

315 isn't a bad temp. They can run cooler, but I'm not bothered with temps until they reach high 300s. Then we begin to watch. And when they hover over 400, then we start taking things apart.

What's unusual is that it's running cooler now than before. Something changed.

A thermal heat gun would corroborate your stack flue temp.

Examples, all different homes:

Bad SFS's, flue temp is confirmed within range -


Sooted heat exchanger:

 

[Garrettmueller]

A thermal heat gun would corroborate your stack flue temp.

Next on the list for sure. That's what I was thinking while standing there. I could touch my hand to the exhaust and the other components when it was shutting down so it could not be very hot. I'm sure the heat gun would confirm.