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How to test a Thermistor - Combi boiler faults - Multi Meter Fault finding
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- Опубликовано: 16 авг 2024
- How to test boiler components. Using a Multi Meter. Testing a thermister. Boiler repair. Today I'm going to show you how to test a thermistor. If you need to test a thermistor in a combi boiler, if you've got problems with the boiler not working or not working correctly, I'm going to show you how to test the thermistor. Combi Boiler Fault Finding.
I've got a few different boilers here. We've got a Baxi 800. I've got an old Baxi Duo-tec. We've also got a Viessmann. We can have a look at some different thermistor in the boilers. We can test them cold and also we'll be able to ... On this boiler here because this one's working, we'll be able to test it hot as well. Just to show you the different readings in the boiler. Let's have a look now.
Before we remove the case we'd make sure that we'd tested it. Done those electrical checks to make sure the boiler's turned off. This boiler's not connected so I know that it's not connected. I'm just going to undo these two screws here.
When we look in the boiler here this is the thermistor here. Baxi call this a Domestic Hot Water NTC sensor. That's what a thermistor is. What we need to do, we need to test this. We need to test ... There's two prongs in there and we need to test this. On this video what I'm going to do is I'm just going to undo this out. On this particular one it's a 13 mm connection. What we do is we just un-clip that off. That's got a little clip on there. Normally we'd just clip that down. Then we'd get a 13 mil spanner. We'd get the 13 mil spanner and then we'd just undo this out of here.
Now just to bear in mind, with this particular boiler, this is a wet pocket. If you disconnect that out of there then you're going to get mains water pressure squirting out of there. You'd need to make sure that you'd turned your water off, and opened your hot tap and made sure no water were flowing through before you did it.
Just another way ... Just before we undo that there you can also ... You could do it on the board if you wanted to. You could remove this cover here. Then if you have a look in the manufacturing instructions you can see where these green wires go to. Then you could test it on board. On this particular one I think it's X400 but we'll just have a check of that. I've been on the Baxi training course and I've got their engineer service manual for this boiler. In the engineer's service manual you can see there the electrical information. You've got you Domestic Hot Water NTC sensor. That's your temperature sensor, your thermistor. If you follow them wires down they'll go to the plug X400 there. If we have a look it's terminals one and terminals three.
If we wanted to we could test it in there. We could put a multimeter into there and test it. But I'm going to take this thermistor out on this so we'll have a look at it. But first of all what I'll do is I'll show you the multimeter and I'll show you how we test it.
A little bit hard to see but I'll just show you this now. I said it was number one and I said it were number three. It's actually number one and it's number four. If you're going to check it at the board you would check it at number one and number four. I'll just get the multimeter now. I'll show you the multimeter.
This is the combi boiler thermistor, or boiler thermistor, or combi boiler sensor, or Baxi temperature sensor, or Baxi thermistor. This is what we're going to test there. If you can have a look on there it's a little bit hard to get in and get onto them wires. What I'm going to do is I'm just going to cut the lead off the boiler, just to make it easier for this test now. But first of all I'm going to show you the multimeter.
If we look on the multimeter I've got a Fluke 114 multimeter. What we want to do we change it to ohms on there. Ohms. Then what we'll do is if we have a look on ... If you can see on there. But that shows you M ohms. When we look at what M ohms means. That's a megaohm. A megaohm is one million ohms.
I've got a little tester block here so I can show you the different readings on there. That one's M ohms. Then if we go to the next one this one now, if you see there is K ohms. If we have a look in the book what K ohms is there, so it's K ohms. That's one thousand ohms. Then if we have a look again, if we go into this one, and we have a look on there. That one, that's just ohms.
You just need to be careful when you're doing your readings that you're seeing the right reading. Let's have a look at the thermistor now.
We've got this thermistor now. I've just cut the lead off out of the boiler. I've just bared the wires back. Obviously you wouldn't normally do that but if we connect this ... If we put it right way round and connect that onto there. Then what we can do now ... This thermistor now is going to give us a reading or it should do if it's working okay.
Hi Allen I am an electrical engineer (retired I feel better now). It is important to isolate the thermistor as you could be reading the circuit PCB if you try testing the resistance with it connected, this may sound obvious but you would be surprised how often this mistake is made.
I actually meant to say to take plug off and test from it. Thanks for the correction 👍
Hi Matey,
So I have been reading that resistance goes up with temperature increase but in this video the chart shows the opposite. Higher the temperature the lower the ohms.
Please advise.
@@nightrider8918
There are two basic types of thermistor. NTC and PTC ( Negative and Positive Temperature Coefficient) and for NTC the resistance goes lower as the temperature increases. For PTC the resistance goes higher when the temperature increases. Note that different types of thermistor can have widely differing resistances at any particular temperature, so you have to get the correct specification of part when replacing these items.
Nice one Allen , I usually cut off the plug leads on the ntc's of replacement boilers I fit and keep them in my spares box as most are the same on all boiler makes and if you have a few different ones you'll find one that fits for testing purposes......👍
Thanks for watching.
Thanks Allen, thank you for all your support !!!
Great job as usual Allen. Thank you for all your support !!!
Thank You
Numba on and farr 😂 quality 👌 great vid as per Alan.
Great video Allen, thanks for taking the time to do these.
Thank you for watching please give the video a like. 👍
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Fantastic video...THANK YOU ALLEN!!!!
My pleasure!
Great video. Very useful. Congratulation Allen.
Very interesting video Alan. keep up the good work 👍
Thank you thermister Hart.
Thank You
brilliant thanks for showing 👍
thanks Allen for sharing this information with us enjoyed the video.
Big thank you to Roy Fugler from Baxi Boilers as he did my refresh training. Thanks.
Superb work really enjoy these videos
Glad you like them!
Hey. Thanks for info!
Great video...very well explained...thank you!!
Thank You
Best video you have done Allen 👍
jmqmin Thanks 🙏
Such a clear and helpful video! Thanks ;-)
Top work Allen NTC aka Negative Temperature Coefficient sensor use them in washing machines. Saved 100 quid call out and put a new NTC for a couple of quid in a friends washing machine.
Tanx for the upload allen best video ntc on youtube👍
Big thank you to Roy Fugler from Baxi Boilers as he did my refresh training. Thanks.
great video thank you for sharing your knowledge...
very helpful, appreciate it man!
Glad it helped!
Great video Allen👍👍
nice one.im not a plumber but very interesting and could come in useful👍
Another great video Alan👍
Thank you.👍
Alan you are a god to me 👏
Thank You
Hi Allen, I understand the relation between ohms and temperature now, but why would you need that information? Is it to test whether the water leaving the tap is the correct temperature that you’ve set on the boiler, for instance, if it’s testing at 50 degrees on the multimeter, would you have to check the actual water temperature at an outlet with a thermometer? And if they aren’t matching, would that mean a fault in the thermistor?
Thank you!
They normally just stop working tbh. Thanks.
Great video. Just a question should the Thermistor have a washer on it. Im changing mine today. New one come through post but no washer?
Hi Alan I’m testing a thermistor on ohms and all I’m getting is the lead resistance. Is this correct if it’s broke
You could have explained that OL on your Multimneter means "Open Line" - (No Circuit).
Thank you.
Great video. Very informative fella. Cheers
If your hot water is running cold then hot , could it be a thermistor fault...
you are the big boss
Thank you.
I changed a thermistor once in the first boiler you showed & snapped the heating pressure sensor off from the block 🤭 it was plastic & very brittle & I was dumb
Merry Christmas
Allen how can I get one of these manuals? I've been on the Baxi course too but they never gave us any manuals.
Hi Allen you best teacher, could you tell me which baxi Breakdwn course is better, I’m trying to find but there are so many choices so which is better and if you have link with that could you write please?
Also does new one need ptfe tape on it?
Hello, my boiler Beretta, would not keep water temperature the same if I shower or even wash hands. Boiler seems to turn off after some time when it "reaches the right temp." so after this water temperature drops few degrees, sometimes drastically. Could this fault be the problem of mine? Thank you
Thanks very much for your comment, please consider subscribing to support the channel 🙂
Old baxi is gold
Thank you for taking the time to watch my video.
Hi Matey,
So I have been reading that resistance goes up with temperature increase but in this video the chart shows the opposite. Higher the temperature the lower the ohms.
Please advise.
Do these drift much over time? Or go from working to complete failure,open circuit or short circuit?
Great teacher as usual , do you need to complete baxi course to get the engineer manual or you can buy from .
Yes.
Thanks for your reply mate stay safe
Always a pleasure. My multimeter cost under a fiver.
Are the cheaper multi meters OK for the odd repair I only need one for a single job of checking the ntcs on my vaillant ecotech plus as there's aa F64 code showing off and on
Thank you for taking the time to watch my video.
Thank you
Thank you for your videos can you upload the manual?
I will try and add it to a video. Thanks.
Hi, do you mean boiler temperature or room temperature please?thanks
Training
please if you can share the engineering book
Thank You
Brilliant video Allen. Finally had my baxi 836 installed last week on your recommendation. Im sure i wont be needing to do this test in a long time.😉. I cant believe how quite it is compared to my ideal isar. Thanks Allen for all your video reviews for helping me decide which boiler to go for. Buy the way how's the loft conversion going?
Loft is going well, It’s all been plastered, Just needs paint. Thanks.
@@AllenHart999 would faulty ntcs cause the boiler fuse spur to blow please Allen? Or is the pcb itself likely to be at fault thanks its a F64 fault code on a vaillant ecotech plus? Your clips are great BTW cheers
Gary Lawton .....Hi , F 61 to F67 fault codes usually indicate a fault with the PCB board and you will more than likely need to change the board...👍
@@yensabi can you test the board somehow?
Gary Lawton ....Not really mate other than a visual inspection to see if there is any obvious damage , best bet is to take it out and get a reconditioned one for about £70 and that way if it's not the board you haven't wasted £ 150 , there are a few company's that do the re con boards , just send in your old one as part ex........👍
How much should a thermistor replacement cost?
Any sparks watching this?
Should subtract LEED resistance
It’s actually terminal 1 and 4 on the diagram. Just a comment
What's going on ere then guv ? I distinctly remember you stating NO ADS in your videos Allen, I've just had three during this one. Thank you for posting though.
No ads on the videos that have been sent in. Some of the videos I do have ads. I spend 2 or 3 days a week doing videos and still have to live, thanks
Allen Hart That’s the trouble with txt you can’t tell the emotional intent of the message sometimes. It was only said in jest, my apologies if it offended you.
Allen would you say that thermistor resistance reading document is service manual?
Oh sorry I miss it u said engineers book Allen thank u.
👍👍👍👍👍
Hi, is it necessary to remove the thermistor to test it? Will it affect the resistance readings if you leave it in place?
No, You can test it in place. Thanks.
@@AllenHart999 That's great, saves me a bit of bother. Thanks! 😁
Great video thanks👍
So obviously if the k Holmes are low when the boilers cold, and vice versa, the thermistor in knackered?
what 'book'??? what if it was a ptc??? ooer
Not sure what you mean? Thanks.
Think he means the thermistor type you said yours was a NTC and sim b mentioned a PTC ,Your type of thermistor is a negative temperature coefficient one (NTC) but you can also get positive temperature coefficient ones (PTC). Basically they are the same devices but work in a reverse manner. Namely the resistance of the positive one goes up with an increase in temperature and the resistance of the negative one goes down with an increase in temperature.
Hi Allen, have you thought about setting up a training academy in your boiler room?
😂😂😂😂
That’s what he is doing
Baxi make it so easy for engineers to diagnose. Including giving you extra references if you do the training course. Why dont Worcester offer this instead of having to mess around on the phone to them everytime😡
Baxi have got rid of some of the trainers now.
@@AllenHart999 oh no really! Well that's a shame. But I'm glad you post what you do Alan. I'm just starting out on faultfinding and your vids are truly so helpful🙏
@@MrHukd Thank You.
What book are you use???
👍👍👍
@@AllenHart999 can you show step by step.how draim boiler
💝💝💝
Someone’s just had a training class from Roy @baxiboilers 😂
That’s not one of his tester choc blocks is it ?
Yes I went on training yesterday to recap, also did the training about 2 years ago. That is Roy’s tester 😂😂😂
Would that be terminal 1 and terminal 4 ? 😉
I cannot remember now 😂😂😂😂Thanks.
Hi Allen my new boiler instructions says 5 inches for the flu hole in the wall. The existing hole from the old boiler is 4.5 in, but a local supplier says the new flu is 4 in (100 mm) dia. Do I still need to re-do the hole so that it's 5 inches for my new Ideal 30+ logic?
Get a gas engineer to do the work 👍
+Hector Heath Make sure you use a gas engineer/plumber it’s not worth it, they will be able to sort the warranty and building regulations, Thanks.
Test in ice water for accuracy
You cam explain your videos in much less time