Pentair Mastertemp 400 Replacement of Thermistor

Thermistor Part #: 42001-00536S
HLS (High Limit Switch) Part #: 42001-0063S

[@FLYBOY123456789]

Thank you fellow pilot...after watching your video...I changed mine an hour ago and noticed the original thermistor was actually cracked and slightly corroded. Got some of the same error codes and spa would not heat up. Bravo - keep 'er straight and level.

[@jazelcabrera3273]

Thank you! Thank you! Thank you! For the step by step instructions. My pool guy was only advising to replace the board again, in which I already had him do this last year. I'm so glad that I came across your video. I replaced the part you advised and now the heater works again!

[@drshane111]

thanks for the video. This helped to know exactly where to look. When I opened the hood, the wires were loose at the control board and on the thermistor causing the E01 error. The thermistor itself was ok. It’s only 2 years old.

[@Easystreet208]

Just want to say thank you! My 250 was reading much cooler than it was

[@hotrailsrose]

Thank YOU ! It worked perfectly, now my wife thinks I'm a Rockstar, thanks to your video.

[@blackburd]

Thank you very much, fixed my heater.

[@sebabasstek5364]

Men you saved me at least 100$ thanks

[@scottbelknap9994]

Thank you, exactly what I needed!!!

[@bharned3]

Thanks again you have saved me twice now allowing me to make these repairs my self saving myself lots of money. How can I buy you a beer

[@pvt-pilot]

Your thanks is enough. That's what makes it worth it to me. Cheers!

[@rickjanik]

Thanks for video. It worked perfect. Heater fired right up. Now I just have to figure out why my membrane will not change temp when using up and down arrows.

[@carlosaceves8186]

Thank you for the info Good video. ☆☆☆☆☆

[@CammedFox]

I THINK this is my (latest) issue with my Mastertemp 400. We inherited this thing with our new house and I just want to take a sledgehammer to it. It has been nothing but chasing issue and issue and we've never been able to enjoy it. Now we have family in from out of town and it decides to crap out 10 mins into being in the spa. Fingers crossed

[@adamfarasati3576]

This worked perfect. Thanks!

[@tangot2]

Great Video. My switch had issues. It would work for a while then suddenly decide it was way hotter than it was and turn the system off. Ease fix. Thanks.

[@goreyboggs]

Mine showing 115 has only about 80°. I ordered it hopefully have it in tomorrow.

[@pvt-pilot]

You are certainly on the right track. High resistance readings on thermistor translates to high temperature readings by control board. Any higher resistance than this, the contol board will see it as a full open (infinite resistance) and result in E01 error. Also, make sure you spade connectors are clean and not corroded so that you have zero resistance across each connector. You don't want something like corrosion to add resistance into the equation while trying to get an accurate reading from a resistance based component such as a thermistor. Cheers!

[@aagalani]

Great video. I am wondering if after market Thermistors would work. The one Pentair sells is very pricey.

[@codytimmons9319]

Thanks for the videos. They have proved helpful. Current problem....heater only heats to 96. I’ve replaced every sensor I know of. The panel knows the actual and requested water temp, the heater shows no error. It is not shutting on and off (frequently) like it would if it were the thermal regulator. I rebuilt the manifold. I’m thinking just fully replace the manifold and circuitboard?

[@pvt-pilot]

You are all over this mate. Did you get it fixed? You have done so much to it that I don't really have any further advice. Sorry I couldn't be of more help.

[@sonkap1]

Great video for the information. I have a question --- I have the same heater for my pool and lately, feel that the spa temp is not as hot as it used to be. I'm not sure about this as the spa hits 104 without problem. It's just that the temp doesn't feel as hot as before. Last year, I would have to sit out of the spa every so often to cool down. Now, I'm in the spa for over an hour and wish it were hotter. Could this be the thermistor?

[@pvt-pilot]

Yes, it certainly could be. If the thermistor is reporting too hot (just like mine was), it will cycle off too early or not turn on at all (mine wouldn't turn on at all. Check the temperature that the thermister is reporting at ambient temp when you first turn the heater on as shown in the video. If it is a high temp relative to what your pool thermometer is reporting, change the thermistor. The thermometer that is drilled into your plumbing that is wired to your main panel reports your pool water temperature and should read about the same as your thermister when you first fire up the heater. You may have noticed my new thermister in the video was 1 degree off in comparison to my pool thermometer. Hope this helps. Cheers!

[@presidentgas4980]

What should the proper resistance be on these thermistors when measured with an ohm meter?

[@viphailservicehailrepairex2777]

My spa doesn't heat beyond 99, and takes a long time to get there (from 65-68) but there are no error codes. Is it likely that it could be these 2 parts?

[@AR-vd3pb]

My heater turns on but the water never gets hot. It just keeps running and will eventually shut off without heating the spa. Could this be because the Thermistor is not working properly? Wondering if I should replace it. Thanks!

[@pvt-pilot]

Not necessarily the thermistor. Are you getting a water temp reading on the control panel display that seems correct? That temp reading is coming from the thermistor, so a defective thermistor would not give a legit water temperature reading. Secondly, are you getting E01 on the heater display? This would indicate an open (broken) thermistor. If not, look on the control board for other error lights (turn the lid of the heater upside down to easliy read the lights). If no error lights are turned on, look for defective non-electrical parts...for example, remove the thermal regulator and test if it opens under hot water (over 120 degrees) and closes with cold water.

[@mariorosales8410]

Hi! I have the same heater, and lately it has been turning on completely on its own, and stays on. It will show 345 as the temp. I know that temp is not accurate so is that a fault code? I then turn off the heater but 30 minutes later it's back on. Any thoughts? Thank you!

[@officerkrupke4966]

Take the side panels off, than remove the four wing nuts holding the top in place. Turn top over and look at control board. There is a ribbon cable connecting the membrane window. Disconnect the membrane cable from board. If this stops your heater from mysteriously turning on by itself, than replace the membrane. The membrane is the front window with the buttons on it. It is held in place by adhesive. Just peel it off to replace. Be careful that you plug new one in the same way the old one came off.

[@realpolicetalk]

Great job very informative.

[@brandycampbell6154]

The screenlogic panel temperature is reading high. I can't even get the heater to turn on. Should I start by doing what you did above? The only part I can find is Thermistor Part #: 42001-0053S, would this work because the one you have listed is different.

[@pvt-pilot]

No, the screenlogic panel has a different thermometer that is connected by a gray wire from a water pipe back to your panel. That thermometer is usually drilled directly into one of your white PVC pipes and has an included O-ring and is often held in place by a wide stainless tie wrap. See if your main panel display shows different temp than your heater display. Replace the thermistor only if your heater is displaying wacko temperatures.

[@pvt-pilot]

The thermometer I am referring to for your main panel can be found here: poolguysupply.com/products/temps-p-10k?gclid=Cj0KCQiAzsz-BRCCARIsANotFgNLe57kc3hBPh-rnDYNGrx6mpGZ6W5DLpunnYKtz-GmhpHLqpf8NzoaAgkTEALw_wcB

[@brandycampbell6154]

@@pvt-pilot Thanks for that link. I found where it is on my equipment. I'm trying to calibrate my pool and spa temps with my screenlogic configuration because I think that might be it but it will not save! Ugh! Do you happen to have a video replacing that thermometer?

[@pvt-pilot]

@@brandycampbell6154 I don't, but I can just tell you. The stainless steel hose clamp that goes around the PVC pipe is the only thing holding it in place. It comes with an O-ring and the hose clamp compresses the thermometer onto the PVC making the water tight seal on the O-ring. The copper wires are molded into the thermometer. All that needs to be done is follow your existing wires back to the panel and install the new one in the same way and tighten the new wires under the same lugs in your panel. No programming is necessary. Results will be immediate.

[@brandycampbell6154]

@@pvt-pilot Thank you so much. Ordered it and will let you know how it goes.

[@slw1hot]

does anyone know where the thermostat wires go? The fence guy accidentally hit the wires and I don't know where they need to go. Obviously the heater cant work with out that thermostat plugged in

[@pvt-pilot]

This video shows where a lot of wires go: kzbin.info/www/bejne/rX_Hc3V-pqpkrNE

[@MrLuigy888]

hello from cabo san lucas mex. hello friend I have a problem with an ETI 400 pentair heater "overheating at the hot air outlet"

[@deeweec7542]

My mastertemp 400 ignites up but goes out after 10 seconds I replaced sensor on exhaust stack ... any ideas I don’t want to buy a new heater ...I have good pressure from pool .

[@pvt-pilot]

Flip the top over, tell me what diagnostic LEDs are illuminated. We'll go from there

[@gunerman]

@@pvt-pilot I have the same problem. There are no diagnostic codes in the panel and neither of the service lights are lit.

[@pvt-pilot]

@@gunerman Test the thermal regulator. It is a non electronic part. It went out on me and I got 20sec run time then shut down with SEEVICE HEATER but no codes displayed on front and no diagnostic LEDs illuminated on the control board.

[@joevolpe6492]

@@pvt-pilot I'm having a similar problem. Had e05 code. Replaced the igniter which tested bad but now I'm getting an AFS light. I can short the sensor and get it to turn on but after a minute it trips the SFS light. I can replace that too but what I'm wondering actually is that the blower doesn't seem to be running as fast as it used to. I took it apart and there's nothing in it. Any ideas on how fast it should be going or how to test?

[@pvt-pilot]

@@joevolpe6492 Hi there, You should not have to short out your AFS to trick it...ever! We all know that for sure, and it's not a good thing to bypass any other safety feature either. So, let's try to get to the bottom of this. Let's try looking for a blockage if air flow first before assuming the motor is not spinning fast enough because I honestly don'tknow how to test the motor for RPMs or what the RPM specs are. If you already watched my AFS video, you may already know that my blockage was a completely flooded heat exchanger tub. I could have just pulled out the bottom bolt of either side of the manifold and let the water drain out. That would have cleared the clog and gotten me through the weekend with a muddy mess by the pool equipment. Perhaps give that a try to see if you have same problem before replacing the blower motor. Let me know your results of the lowest bolt removal on the manifold and we will go from there. It takes a 13mm to pull one out.

[@rustygrunwald]

is this a the same thing as a low limit switch? versus the other switch for high limit?

[@pvt-pilot]

The thermistor itself? No, not exactly. it is a thermometer that talks to your control board. However, your control board then can act like a thermistat which is, in a strange way now that you mention it, a "low limit switch" based on the digitally displayed heat setting. Water too cold = heat turns on. As opposed to the high limit switch, water too hot = turns heat off. Interesting way to put it.

[@cobrafoaminsertsandcases6060]

Good video. I am getting a g19 error after the 128 shows on the screen. Any idea what that is?

[@pvt-pilot]

Never heard of g19, I would expect r19 after the 128, just to indicate "revision" software number for your control board, but not g19. Sorry, I dont know what direction to point you on that one.

[@cobrafoaminsertsandcases6060]

@@pvt-pilot sorry. Typo. R13

[@jasonlightbearer335]

Hello what’s led 11 for ? Thanks in advanced

[@pvt-pilot]

Each numbered LED is visible from both sides of the control board. So when LED11 is illuminated, you will see that it lines up with the small clear window on the front panel labeled "SERVICE HEATER". LED11 is your light bulb for the SERVICE HEATER light. So.... LED 11 = SERVICE HEATER LED 6 = SERVICE SYSTEM LED 8 = HEATING LED 10 = SPA ON LED 9 = POOL ON

[@jasonlightbearer335]

In that case I’m lost because it’s not giving me any other lights . System turns on then goes off after like 10 minutes . Thanks in advanced for such quick response. 🙏

[@pvt-pilot]

@JASON Light bearer You might have a corroded thermal regulator. It is not an electronic component, so there is no code for it. However, if it seizes up, your heater will notice the water output getting too hot because its job is to open above 120 degrees (scalding temperature) and let cold water bypass the heat coils directly to the output to dilute the superheated water heading to your spa. Safety in mind, check that thermal regulator with scalding hot water and make sure it moves freely. If you need to know how to test/replace the thermal regulator, you might watch my other video: kzbin.info/www/bejne/aXa1nnh-nZ19Z9U

[@jasonlightbearer335]

@@pvt-pilot thanks again for the quick reply . I must say like earlier I mentioned it turns on but doesn’t ignite and then it turns off . So all is turning on is blower .

[@pvt-pilot]

@JASON Light bearer Ah, I did not recall reading that it did not ignite at all, but that is a very important detail. That steers me in a different direction. Let's try a few other things then. 1. Remove the lowest bolt of your manifold, either side, using a 13mm socket. See if any water comes out of the bolt hole when it is removed. If no water comes out, your expensive copper heat coils are good and have no leaks. If water pours out, then there is likely water filled to the top of the combustion chamber. If this is the case, your igniter will be submerged and will be impossible to ignite (your stated symptom), and there will also be no air space available to host the fire party inside. I don't think this will be the case because it should also throw an AFS light when the combustion chamber is blocked full of water because there is no path for the air to move toward the exhaust, and you already said there is no other error light. Just do the bolt removal method to be sure. 2. Check for a defective open igniter using an ohm meter. No ignition could be caused by corroded ignition wiring or broken igniter element. The harness is fairly durable, but the element in the combustion chamber is fragile. If you get infinite ohms resistance (open reading), your igniter must be replaced. 3. There is an electrical box mounted between the combustion chamber and the control board. I don't know much about how it functions, but I think it is called an ICM. (Ignition Control Module). I have never had to do anything with mine, so I won't talk/teach on unfamiliar topics here, but I think there is a short instruction page mounted inside. It references the red LED inside. Blinking once means something, blinking 3 times repeatedly means something. It has been years since I read the notes on that part, but I would read up on that to see if the LED inside tells you diagnostic information. If I think of something else to try, I'll let you know. Good night for now.

[@deeweec7542]

Reading e05 code ..

[@pvt-pilot]

That is an open Stack Flue Sensor. Check your leads to the sensor on the side of the exhaust pipe and/or replace the sensor.