Replace 220VAC Thermostat - Page 1
Forum section: electronics / beginners

author: Larsson55
author_rank: Regular Contributor
timestamp: January 18, 2025, 05:46:01 am
content: About 12 years ago I installed SunTouch electric floor heating under the ceramics floor in one of my bathrooms and so far it has been working with no problem. Now I discover the thermostat (shown in the attached picture) stays always ON, even after a reset. SunTouch does not sell these thermostats anymore, they only have ones controlled by smart phones which I do not want. Can I install a regular 220VAC thermostat which I can get locally for $20.00? (I have similar all over my house)Thanks

author: inse
author_rank: Super Contributor
timestamp: January 18, 2025, 06:29:28 am
content: The thermo sensor is below the tiles on my heating, you have to check how this is compatible to a different thermostat (if it’s the same setup at your place).Check whether there is a problem with the sensor (I expect a NTC) and how you would deal with that.BTW, did you try to repair the thermostat yet, it shouldn‘t be too complex

author: Larsson55
author_rank: Regular Contributor
timestamp: January 18, 2025, 07:43:41 am
content: Thanks for your time inse, I am not an electrician and so I try to be careful with any electrical work I do however I thought any 220VAC thermostat will probably do the same job. Now you mentioned to check the thermo sensor for compatibility and you are right. My sensors (there are 2 as I can see from pictures I took during the installation) are under the ceramic floor tiles and obviously I will hate to brake the ceramic floor tiles. Is there a way to check this sensor from the wires behind the thermostat?Also what is "I expect a NTC" ?Thank you

author: inse
author_rank: Super Contributor
timestamp: January 18, 2025, 09:07:13 am
content: If you have a multimeter, you can measure the resistance (NTC is a resistor) of the sensors.MAKE SURE TO SWITCH OFF THE BREAKER OF THE AFFECTED CIRCUIT B E F O R E!

author: timeandfrequency
author_rank: Frequent Contributor
timestamp: January 18, 2025, 09:34:51 am
content: Hello Larsson55, (hello inse)... and you should read a value between5 k and 30 k Ohms, depending on the current temperature of the floor.Inse is probably right : a newer model from the same branduses a 10k NTC. Search for 'Floor Sensor' in the document.If heat is always on, the relay contacts might be welded shut. Replacing the relay might repair the device.Something similar from Schneider Electric, but no information if the compliant sensor is a 10 k NTC.https://www.123elec.com/schneider-odace-mecanisme-thermostat-fil-pilote-a-ecran-tactile-noir-s520509.htmlhttps://www.se.com/fr/fr/product/S520509/odace-thermostat-fil-pilote-%C3%A0-ecran-tactile-noir/

author: Larsson55
author_rank: Regular Contributor
timestamp: January 18, 2025, 11:05:57 am
content: My thanks to both, the thermostat is OFF now but I have not started any work on it due to other projects. Today Saturday I plan to cut the power OFF and remove the thermostat to see what is behind. Looking in my notes and picture attached I see that I have 2 sensor and one is a spare. So if I am lucky and the connected sensor is not good then I can connect the spare sensor. I will post the results when I am ready.

author: Gyro
author_rank: Super Contributor
timestamp: January 18, 2025, 11:24:28 am
content: Itshouldbe standard reputable installer practice to fit the spare underfloor temperature sensor. Hopefully swapping to the other one will solve the problem, or at least allow you to compare their resistances and so, localize the fault to sensor or thermostat.

author: Larsson55
author_rank: Regular Contributor
timestamp: January 18, 2025, 04:51:51 pm
content: Thanks Chris, is there a way to test the thermostat alone?And how do I find out if a regular heating thermostat like the ones I have all over my house will do the job? These thermostats are the same regardless the size of the baseboard heaters which vary from 500 to 2000 Watts.I remember for the bathroom heated floor thermostat I paid CAD$ 112.00 about 12 years ago so now they must be close to 150.00, assuming I can find one.I attach 2 tables which maybe useful for any answers, my heated floor space is about 24 square feet.

author: Gyro
author_rank: Super Contributor
timestamp: January 18, 2025, 05:28:41 pm
content: In theory, you should be able to wire a potentiometer (wired as a variable resistor) of say, 20k based on your table, across the temperature sensor terminals. I say in theory because the sensor terminals are almost certainly not mains isolated, so you are exposing yourself to a significant risk.I would still choose the method of measuring the resistances of the disconnected temperature sensors and checking that they are the same, within a reasonable tolerance, and are sensible for the floor temperature. That way, you can spot a faulty sensor, or if they match then the thermostat is faulty by default. A much safer method.In situations like this, there is a good chance that the fault is a failed mains dropper capacitor in the thermostat. If you cansafelyisolate the mains and get a photo of the circuit board, we may be able to point you in the right direction to repair (or get someone else to repair) it, rather than replace it. Do the sensor tests first though to avoid blind alleys.

author: Hr_Satch
author_rank: Contributor
timestamp: January 18, 2025, 05:34:13 pm
content: Hi, thermostats, are not 220Vac, it can also run on lower, or even DC,it has a switching contact, to bridge the power.This can be simply a relay, or a TRIAC, bi-directional SCR, . . .if the Temp sensor is good, it ca, also be the output that remains closed.WATCHOUT: electricity can kill you !If the actual broken Tstat has internal electronics:you should first check whether it has its low voltage power supply voltages ;-?Otherwise open your wallet & buy a now one , ding-dong

author: inse
author_rank: Super Contributor
timestamp: January 18, 2025, 06:47:21 pm
content: Hr_Satch, your satements may be true for a pure electromechanical thermostat but not for an electronic one.Triac/Thyristor and DC is a discrepancy per se.

author: Larsson55
author_rank: Regular Contributor
timestamp: January 18, 2025, 10:30:52 pm
content: Did some work on the T'Stat and I attach some pictures. First I turned the main panel breaker OFF (this breaker controls the heating for 2 rooms + this bathroom) but when I removed the T'Stat and noticed all the wiring inside I decided to turn OFF the power to the house since I was not sure if I still had some live wires. I disconnected the 2 sensor wires and set my meter switch to 200K and taken the reading I got 12.6. Sorry but I'm not familiar with the readings but I assume this number means 12600 Ohms?Next step is to make a drawing marking where all wiring is going so I can pull them out and get the 2 spare sensor wiring which I can see them at the very back of the junction box. Since it was getting dark outside I decided to do this work tomorrow.Chris mentioned in an earlier post the possibility to repair the thermostat but my capabilities soldering on a PCB are very limited + to find the right part on the web etc. it will be difficult. I will post more news tomorrow.

author: Poroit
author_rank: Frequent Contributor
timestamp: January 19, 2025, 02:46:17 am
content: G'day Larsson55,Base on your Resistance measurement of 12.6K ohms (12,600) your NTC sensor looks OK and the floor temperature is between 18°-24°C which is probably not bad for Canada at this time of the yearThe chart you posted says sensor has a Typical Value of 10K ohms @ 24°C.I wonder if thereTypicalis actually 10K @ 25°C as this is more common.

author: Larsson55
author_rank: Regular Contributor
timestamp: January 19, 2025, 03:07:59 am
content: Quote from: Poroit on January 19, 2025, 02:46:17 amThanks Poroit, I tend to believe that the sensors are good and will verify tomorrow however that means the T'Stat is no good and replacing it we are talking about CAD$200 assuming I can find one. That's a lot of money for a T'Stat and I wonder if there is a way to scrap this kind of T'Stat and replacing it with the ones I have in my house electrical heating.

author: inse
author_rank: Super Contributor
timestamp: January 19, 2025, 04:13:11 am
content: As I see it, there is a principal difference between thermostats (TS): for room heating, the ambient temp is measured via internal sensor while the TS for floor heating has an external sensor.It is questionable wheter it’s possible to convert one type to the other.Why not have a look at the failed TS whether it’s repairable…

author: Larsson55
author_rank: Regular Contributor
timestamp: January 19, 2025, 05:29:45 am
content: Quote from: inse on January 19, 2025, 04:13:11 amIt makes sense what you are saying inse but in my area there are no places to do this kind of work. Years ago I knew a few and actually used them to fix a toaster + a Sony radio I had but they all are gone now cause not enough business to keep them going. I also understand the principle of how each type TS senses the heat. Most likely when we discover that my TS is bad I will have to bite the bullet and buy a new one

author: WattsThat
author_rank: Frequent Contributor
timestamp: January 19, 2025, 06:45:49 am
content: If your are unsuccessful/unable to repair, any of the standard floor heat temperature control units available on Amazon and elsewhere are compatible with your floor system.https://www.amazon.com/dp/B083XWF2SS/ref=sspa_dk_detail_2

author: Larsson55
author_rank: Regular Contributor
timestamp: January 19, 2025, 07:06:22 am
content: Quote from: WattsThat on January 19, 2025, 06:45:49 amThat's an excellent idea mate I never thought about it.Many thanks

author: timeandfrequency
author_rank: Frequent Contributor
timestamp: January 19, 2025, 10:26:52 am
content: Quote from: Poroit on January 19, 2025, 02:46:17 amYes, '24°C' might even be a typo, or a way to encourage to buy their sensors^^.Because 9k7 NTCs (that show about 10 k @ 2425°C) arenot that common. All of the 9k7 NTCs are non stock at Mouser.If they really used a 9k7 NTC, around 25°C ± 5 °C, the error vs a vanilla 10 k NTC should be about 2%.Not an issue for the current heated floor application.

author: Hr_Satch
author_rank: Contributor
timestamp: January 19, 2025, 11:39:51 am
content: Hi Larrson-55,to your question whether to be able to use a standard home Tstat,I think yes you can, because in the end it all turns about the ambient temp. ain't it ?As to your complaint that it stays on: that's due to some power switch remains closed:shot Triac, or stuck closed contacts from a relay.If you'd find the culprit, and can open the power circuit, than you also know where toplace an interrupting switching device ;-?I think the infloor sensor, is to avoid your bare feet burning on the floor, . . .Some home wall tstats, do allow for multiple sensor inputs.Dunno, whether this helps.But one thing I know for sure: when you find your ways of interrupting the power circuit,you where to go from further on.But all depend also on what power is derived, how many Amps you'll need to d-switch, etc . . .

author: Larsson55
author_rank: Regular Contributor
timestamp: January 19, 2025, 04:13:06 pm
content: Both sensor reading are identical, 12.4 to 12.8 so I connected the other sensor which was never used before and now the thermostat works! To my opinion is not the sensor or the thermostat but rather the connection of these 2 sensor wires which are quite small (about 24 or 26 AWG?) and most likely didn't make a good contact. Also took a picture of the PCB which is attached.