Buderus R2107 displaying outside air sensor error "OA Sensor ERR"

Bobbyd2727

Just noticed since yesterdays storm this error display on my logamatic. the system is still heating the house well. i was just wondering if this may be related to the fact that the outside sensor was vovered with some snow. i have cleaned the snow off but I still have the error displayed. Should I give it a day or so before I call for service?

Grallert

If the wiring is sound from point A to point B it's likely that the OA sensor is faulty. simple and straight forward repair.

GW

If you have tools then ohm the sensor. There is a chart in the manual to match ohms with temperature You likely are losing the outdoor reset functionality at this time .

Bobbyd2727

I have a new sensor. How exactly do you replace it

GW

Just pull off the plastic cover, it should be just a two screwdriver job

Bobbyd2727

What about the electrical hookup? there is a wire going into some kind of small black device. Do I have to shut off the power before opening this? I assume I have to unhook the wire from this somehow and connect it to the new sensor?

GW

This is just an ohm sensor. Most wouldn't bother killing the power because there is no real voltage present. Keep things simple and just change the sensor itself. Leave the old plastic housing.

If you're spooked about wires then sure, kill the power .

Yes you need a small tiny flat tip screwdriver. Many techs have this tool on their person during work hours. I sure do.

Bobbyd2727

Thank you very much! I assume once I get the small black sensor open it will be self explanatory how to remove the wiring and rewire the new sensor?

GW

I should be pretty basic, but since you have a new one you can take it apart to better understand what I'm saying. I must say the Buderus outdoor sensor is a bit finicky, removing the plastic cover off its base.

ajnonn

Hi, my buderus heater is not working , came home from work and it had an Err OA sensor----I desperately need a plummer who is honest and knows how to correct this for me asap , I am afraid my pipes will freeze.

Grallert

ajnonn said:

Hi, my buderus heater is not working , came home from work and it had an Err OA sensor----I desperately need a plummer who is honest and knows how to correct this for me asap , I am afraid my pipes will freeze.

That control should default to a out door air temp of I think zero when the sensor fails, which it most likely has. That control also has a manual setting you can activate, it's the picture of a hand. Push that and the burner should fire. On the left is a dial turn that to about 140 so you don't domestic hot water that is screaming and dangerously hot. The sensor is an easy fix. Start there. It's a pretty common fault and can be caused by a cut wire or loose wire connection somewhere.

heathead

I am on my second outdoor air sensor in 8 years. When it failed the first time got buderus original part, that just failed. I also got generic sensor thermsister, those didn’t work just now got them to have as spares. That didn’t work. Will viessmann tank sensor work. Please PM me if you have good link for spares on eBay for just the thermistor. Now need to find buderus sensor in am before leaving lake house. parts houses in zip code 07871 that might have this? Thanks

kcopp

That sensor is still available.
supplyhouse.com or a Buderus wholesaler will have them.
If it is failing prematurely it could be installed in a way where water is entering the box.
Make sure all holes are sealed up.

heathead

Have one on the way supply house has express delivery by 11am if ordered by midnight for my area. I would have never thought that, must be all owned by same parent company as local supply houses. I would love to know the China thermistor value. The sensor is dry cover and looked lgood. Every time this sensor goes down pipes freeze. Oil company fixed pipes last winter when they froze and other family was at the house. I put the pieces together why when I came to the lake house now and turned on the heat. I had set the warm weather shut down to 87. The sensor must have been way off and turn circulation pump off thinking it’s summer. Need to yankiee engineer a option to know how to keep the constant circulation pump running. WiFi Thermostat never showed it dropping below freezing. But it must have in places for pipes as old house. Or could have been power outage.

NY_Rob

^ NTC (Negative Temperature Coefficient) thermistors are commonly used for boiler control. They are generally rated at 25C (77F), so if you measure the resistance of your new ODR at or near 77F you will find it's rated resistance value.
Alternately, you can look at the ODR sensor chart in the install manual- look at the resistance value at 77F... that will tell you the thermistor value in ohms.
Most likely a 10K Ohm NTC thermistor, but could also be a 5K Ohm NTC type- but you have to measure it's resistance at or near 77F or consult the boiler sensor chart.

As an example of using the chart- take a look below at the sensor chart for the HTP UFT boilers... both the ODR and Indirect tank sensors are 10K ohm NTC types easily obtainable on ebay for $1 or less.




For outdoor use I've had good results with the cylindrical type thermistors vs. the tiny bead type found inside t-stats and indoor digital thermometers. The added mass of the metal sleeve prevents rapid temperature excursions due to wind, etc.

GW

good to know!

MyDirtIsRed

Used this to replace my ailing thermistor a couple of weeks ago:

https://www.digikey.com/product-detail/en/murata-electronics-north-america/NXRT15XV103FA1B040/490-7171-ND/3900395

The AM10 manual has a table that allows you to calculate the thermistor parameters, and this one works nicely.

AndyFrew

Hello...the sensor is dry cover and looked lgood. Every time this sensor goes down pipes freeze. Oil company fixed pipes last winter when they froze and other family was at the house. I put the pieces together why when I came to the lake house now and turned on the heat. I had set the warm weather shut down to 87. The sensor must have been way off and turn circulation pump off thinking it’s summer.

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