Vitodens 100 boiler not working & flashing 18


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Old 01-01-20, 09:56 AM
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Vitodens 100 boiler not working & flashing 18

Often the heat will not be keep up & when I check the boiler it will inactive and flashing ď18.Ē I looked it up & it says the outside temp sensor is broken?

Im not a plumber but Iím pretty capable, I was hoping that with some direction, I could fix it myself. I fixed a broken mixing valve last year with the help of this site....hoping for a repeat . Thanks to this site & the contributors for any help!
 
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Old 01-01-20, 10:12 AM
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That's correct..... outside temperature sensor line open. You will need a test meter with ohms to test for that problem. The steps are shown on page 63 of the manual. The chart shows the resistance you should measure. It's based on outside temperature.

Vitoden manual (pdf)
 
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Old 01-02-20, 09:32 AM
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Thx! I will follow up & report back...

u r the man Pj
 
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Old 01-02-20, 02:57 PM
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Resistance

So on terminals 2 & 3 I get 2.4 kohms & itís 35 outside. That is with the boiler running. I didnít think to shut it off and try it. The chart says I should be around 35kohms for that temp if Iím reading it right.
 
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Old 01-03-20, 10:14 AM
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Hi, boiler running or not will make no difference, you should be removing the conductors from 3,4 and taking your reading between them.
 
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Old 01-03-20, 11:41 AM
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I started with 3 & 4 I get no reading at all, so I tried every other option. 3/4 is reading 0

So assuming that is the problem, is this a fix I need to call Veissman for?
 
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Old 01-03-20, 01:00 PM
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Hi, I am not familiar with that sensor, it maybe that just the sensor can be replaced outside, I would contact Veissman tech support and ask the question, how old is the system, could still be on warranty.
Check outside and see if by chance there is a loose connection at the sensor.
Geo
 
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Old 01-03-20, 10:02 PM
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I agree with Geo...... check out the outside sensor connections. There may be an outside splice.
 
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Old 01-06-20, 07:55 AM
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So the outside piece appears to be fine, there is nothing corroded or loose. I’m going to cut the wires, re-strip, & re-connect to see if it’s the connection. If not, it would appear to be the actual sensor outside, which Veissman says to replace if the k-ohms reading has deviated too far from that chart (which it has).

The sensor & wire look easy enough to replace if I need to, but I can’t find the actual part.
 
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Old 01-08-20, 06:31 PM
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Viessman has discontinued that part.
Viessmann 7508904 Sensor #1 (outdoor NTC) 10K

I wouldn't even bother looking for one of their over priced replacement kits.
Go right to Ebay and buy the raw part you need. You need a 10KΩ NTC sensor.
There are many choices.Get a five pack.

5 pack NTC sensors
 
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Old 01-10-20, 01:48 PM
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So when I stripped the wires I could see that they were oxidized, in my initial look, I didn’t actually take the wires off. So I cut them, stripped & reconnected & the flashing “18” has stopped. We have also had a few very cold days recently & the heat is keeping up now. So it appears to be fixed..

Just for academic purposes though, I measured the resistance again & on those 3/4 terminals, I still get nothing, so I’m not sure if I’m doing something wrong there.
 
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Old 01-10-20, 03:18 PM
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Hi, measure the resistance at the sensor with the wires from it, next remove the wires from terminals 3-4 , twist those wires together and go outside to the sensor and take a reading across those 2 wires.
Geo
 
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Old 01-10-20, 06:38 PM
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You cannot check the resistance to that sensor with it connected to the controller as it runs voltage thru it. You need a meter that can read 10k ohms of resistance. A digital meter on auto should be good..... or an analog meter on Rx100.
 
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Old 02-26-20, 09:20 AM
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So an update....

I figured out why the reading was not showing up. I have two outside temperature sensors (I didn't realize that until recently)...one goes to my Taco mixing valve (will open a new post about that shortly) and the other is for the Viessman boiler.

One of the outside temperature sensors was absolutely obliterated, so much so that I thought it was from before I bought the house, it couldn't possibly be only 10 years old. And I thought I only had one sensor, so due to the time frame it was installed, I assumed the clean, unbroken sensor was it....I was wrong. That sensor, which goes to the mixing valve, its connections were oxidized, but I stripped and reconnected the wires and the flashing 18 went away. Not sure why however bc after tracing the wires, the obliterated sensor is the one connected to the boiler. That was why I was still getting a 0.000 reading on the meter. So I replaced it, and everything is working well again, it also measures resistance in the proper range now. I do have a Q about the mixing valve but I will start a new post for search purposes.

Thank you all so much. I really love this place!
 
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Old 02-27-20, 11:47 AM
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Many of these sensor are a generic 10K type. For $10 this might be worth a try: https://www.supplyhouse.com/Rheem-PD...10K-Ohm-Sensor
 
 

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