Buderus gb142 with outdoor reset and nest

JJTraxx

I've had a buderus gb142-30 with the am10 outdoor reset for about 9 years and it's been working well. I've had a dumb thermostat and I want to switch to a smart thermostat and bought a nest 3rd generation. I have no intention of using the learning or programming features, but I really want the wifi and alerts for my phone. Old thermostat had 2 wires only. Rh and W. No C wire. I bought the nest because it was supposed to work with most 2 wire systems with no C wire. This is a heat only application. Mine didn't. I bought a 24v transformer and connected that to the C and Rc terminals on the nest. Still no good. Thermostat calls for heat while testing it from within the nest. The outdoor reset seems to be complicating things. I've turned the temperature shutoff all of the way up so the am10 wouldn't stop the call for heat. Boiler never fires. DHW calls work fine.  I've looked around online and found some people use a 24v relay to affect the call for heat to the boiler as shown in the picture above. I don't know anything about relays. Can anyone offer any help? 

HomerJSmith

Your diagram is correct. Don't connect the common on the transformer to the Rc connection on the nest and remove any jumper between the Rh and the Rc. Nest has technical help if you call them. Use this relay, it's cheap.
https://www.supplyhouse.com/Jard-92290-SPST-24V-General-Purpose-Switching-Relay

If you have a transformer mounted on a 4X4 metal box you can use this relay.
https://www.supplyhouse.com/Functional-Devices-RIBU1C-Enclosed-Pilot-Relay-10-Amp-SPDT-w-10-30-Vac-DC-120-Vac-Coil

Without looking, your Buderus circuit board is going to control the outdoor reset based upon programing. It may have a warm weather shut down. In shut down mode the Nest won't turn on the boiler.

By connecting the transformer Common to the Rc you may have fried the transformer or damaged the Nest. In this case, c stands for cooling not common.

TAG

Why mess with the ODR ? What did the dumb thermostat do ... I had one of those years ago and it had a built in night setting

JJTraxx

The dumb thermostat worked fine. No issues.  I really need the wifi only from the nest. 

JJTraxx

Thanks for the in depth information Homer. The first relay... Does it need to be supplied 120v current or simply the 24v from the transformer? I got a plug in transformer with the bare wire leads. The 2 wires going to the nest come from the am10, not the boiler board. The am10 is in between the boiler and thermostat. The transformer is still fine and so is the nest. Should I use the thermostat takeoff from the am10 instead of the WA terminals on the boiler? I literally know nothing about relays. 

Jamie Hall

If all you need from the Nest is the wi-fi, be sure and take a deep dive into its settings and kill ALL the smart features. They will fight with the ODR and make you, your boiler, and your checkbook miserable. Better yet, figure out what it is you really want the wi-fi for, and get a device made for that and get rid of the Nest entirely. Or just disconnect it from the heating system.

JJTraxx

Thank you Jamie. I'm well aware of not using a smart thermostat with a modcon boiler. I have disables all of the smart features. I simply want remote access from our phones for when the wifey is cold and to keep an eye on the temp when we're not home. In addition, I'm looking down the road to what people want when I sell the house in a few years. 

TAG

I still don't understand what or how you used an additional thermostat -- was it some sort of a kill switch?

The whole point of the ODR is to dial in the boiler so it reacts to the outside temps keeping the house the temp you want. They do make an optional wall control for that boiler -- looks like a room thermostat .... but, it's really modulating the curve based on how you have it set.

JJTraxx

OK Tag. I'll restate what's going on. I have a buderus gb142-30 with a wall mounted am10 outdoor reset control heating 1 zone. It has only 1 thermostat that I'm in the process of replacing from dumb with 2 wires. Replacing my 1 and only thermostat with the nest generation 3. Since the wires that run to the thermostat come from the "thermostat looking" basement wall mounted am10 odr and not directly from the boiler, it complicates the nest installation.  I'm simply adding remote phone access to my heating. It's a simple idea. Not sure what you don't get? You don't have to agree with my choice or my needs. Looking for help and not criticism. 

JJTraxx

Homer.... This is the transformer I got

TAG

Sorry -- not trying to tell you what to do. I know at one point the AM10 was an option and then later it was supplied standard -- part of the boiler. Doing a quick look -- I must have had the 35 room controller on the early one when it was an option. My second must have been jumped as it used constant circulation .. no inside thermostat.

The contacts on AM10 will have power in them -- so you don't want to send anything through that pathway. They just want to be jumped. The AM10 tells the boiler to fire based on the curve. Attaching to the boiler direct will eliminate all the reset. Did you other thermostat have batteries ?

The wiring diagram for the AM10 should show how to power a thermostat -- looks to be lacking. In Germany it would be an on off switch.

Only one of the AM10's contacts will show power ...

JJTraxx

Tag... Thank you for that. Yes, the old thermostat had batteries. The thermostat terminal on the am10 is the middle set. I'll check for power when I get a chance 

JJTraxx

Jamie Hall

If I may, I would suggest powering the Nest with the adaptor you got rather than trying to power it from the AM10. That way you will be using only the Nest on/off output, unpowered (R and W I think), and it will behave -- from that standpoint -- just like any two wire thermostat. Not that it can't necessarily be powered from the AM10, but you would need to find out which terminals on the AM10 offer constant 24 VAC power out, and that is somewhat less than obvious.

HomerJSmith

I bought the nest because it was supposed to work with most 2 wire systems with no C wire.

Using a Nest without a C wire can be problematic even tho it is advertised as not needing one. If you only have 2 wires to the old thermo check the cable connected to the back of the old thermo as some multi-cables have the extra unused conductors wrapped around the cable.

I'm not sure that the wall trans that you pictured would have enough power to support a Nest and a relay coil. It is only 300 milli-amps, but it probably does. The RIB relay has a coil draw of 28mA. I don't have the current draw of the Jard relay, but I expect it to be almost the same. Are you planning to wire your trans at the thermostat if you don't have a third wire? Without a relay there might be a phasing conflict if you do, you want it in phase with the AM 10 transformer power. With a relay no problema. (a little Spanish lingo) The point contacts from the relay go to the TT connections on the AM 10 module that you pictured.

I assume you want to use the AM 10 with the outdoor reset and the drawing of the AM 10 module is correct. I would wire it this way.

JJTraxx

I really appreciate the help guys. Homer...  The plug in transformer I have has wires 23' long. Gonna plug it in in the basement by the boiler. I bought new 18/5 thermostat wire and I'm gonna fish it up to the thermostat location above to make just the crappy wire that's in the wall now isn't the problem too. If I'm understanding your drawing correctly, the non coil side of the relay connects to the 2 contacts on the am10 for thermostat. The coil side... The white wire to the W terminal on the nest with the other terminal on the transformer going to 1 leg of the transformer. The other leg of the transformer would then go to the Rh terminal on the nest? 

Jamie Hall

got it

JJTraxx

OK, so the plot thickens. I just had my annual service done on the boiler this past Saturday. When he went to check the flue gases, he couldn't get the boiler to fire with the thermostat turned up and the outdoor shutoff temp on the am10 turned all of the way up as well. He had me open several hot water faucets to drain down my indirect water storage tank to get the boiler to fire for dhw. I should have know something was up then.  I wound up putting the old, dumb, battery powered thermostat back in and connected directly to the WA terminals on the boiler. Disconnected the am10 completely. Boiler answers call for heat and then properly shuts off when thermostat turned back down. The Am10 must be bad. I don't think it's the thermistor in the temperature sensor because it was reading close to accurate. Also didn't have any constant voltage on any sets of terminal on the am10. Since buderus had discontinued the am10, now I have a non-modulating boiler. No Bueno. Any ideas for a replacement for the am10? I have the relay coming tomorrow, the nest, and new wire. I love a challenge as long as I don't break anything. 

HomerJSmith

Don't forget the C wire. I wouldn't be so quick to dismiss the AM10. Disconnect the outdoor sensor at the AM10 and jump the TT connections on the AM10. Does the boiler turn on?

JJTraxx

I disconnected the outdoor sensor at the am10 and jumped the tt connections at the am10. Boiler fired. I also fished new 5 conductor wire to the old thermostat. The old one had 2 splices in the wall. Right now the old thermostat is connected as well as the am10 with the outdoor sensor disconnected at the am10. Boiler seems to function fine and responds to calls for heat from the old thermostat and properly shuts down when the thermostat is turned back down. Does that mean that the am10 is fine and it's the outdoor sensor that's bad? 

TAG

I'm wondering if you damaged something when you connected the transformer to the nest and the AM10.

Since it's warm out you need to either energize the DHW circuit or I think the manual will tell you how to test. Above 70 degrees outside the boiler will not fire and under this is will not fire unless the water temp is under the curve you have set.

Those terminals sort of work as a switch or high inside temp limit -- when I lived in Germany it was for night setback if the ODR did not have a night mode.

JJTraxx

Tag... I never connected the transformer to the am10. It was connected only to the nest at the rc and c terminals. The rc terminal is only for cooling, so it should be isolated from the rc. No jumper. The boiler service fail to fire for heat demand happened before I touched anything

HomerJSmith

Yup, most probably good. I would measure the ohm reading of the outdoor sensor with the sensor disconnected. It should be close to the temperature chart. You can look at the programing in the 5th menu level, too.

HomerJSmith

Fishing in a 5 conductor 18ga cable, you don't need a wall transformer but can use a 15-40VA transformer at the location of the AM10 and boiler. The wiring would be the same as my diagram only you would run the power and the Common up the new cable to the Nest.

JJTraxx

The outdoor sensor was measuring 7.25 k ohms, which is about right for 90 degrees. So that's good too? I'm really not good at schematics Homer. This is the transformer I have again. I bought the jard relay you suggested. Arriving today. If I mount the relay down nest to the boiler and am10, could you please tell me exactly what to wire to where. From your drawing I know to connect both terminals of the non-coil side of the relay to the 2 tt screws on the am10. 1 leg from the coils side of the relay goes to the W terminal on nest. For the transformer  1 leg to other terminal coil side of relay and other leg of transformer to rh on nest. Do I piggyback a wire to the non W coil side of the relay to c terminal on nest? I can't tell you how much I appreciate your help and time. Also... The 2 transformer wires. 1 has lines on it and the other has nothing. I thought with 24v they are interchangeable 

JJTraxx

OK the jard relay arrived.  Non coil side of relay has both terminals connected to tt terminals on am10. On the coil side of the relay 1 is going to 1 leg of transformer. Other coil terminal is going to W terminal on nest. 2nd leg of transformer is going to rh on nest. Not sure what to do for the c wire in your drawing Homer to get c to the nest

HomerJSmith

For the charging circuit use the green conductor in the new thermo cable. Connect one end to the C connection on the Nest. Connect the other end of the green conductor to the the transformer wire that connects to the relay coil #1.

The circuit is as follows: Power goes from one leg of the transformer to the Rh connection on the nest--thru the Nest circuit to the W1 connection to the coil #3 tab then thru the coil to the other transformer lead. That is an operational circuit.

The charging C circuit is as follows: Power goes from the one leg of the transformer to the Rh connection on the Nest--thru the Nest charging circuit to the C connection wire to the other transformer lead that is connected to the #1 tab on the relay. That is a charging circuit.
Check your programing of level #5 for the out door reset. Resistance looks good so the sensor is ok.

JJTraxx

So relay coil 1 has 2 wires connected to it? C wire to c terminal on nest and 1 leg of transformer?  By program level 5 you mean the outdoor temperature cutoff? I currently have it turned up as high as it goes (86) to enable boiler firing for my thermostat install testing purpose. Normally I keep it at 70. I used the blue wire for c wire to nest as I am used to c wire being blue. I just want to make sure it's all correct before I reconnect the am10 to the boiler. Just to make sure... The leg of the transformer that goes to the rh nest terminal also has the c wire on the same coil #1? Or should the c wire to the nest share terminal #3 with the W1 wire? I don't want to fry things. Waiting until I hear back from you before I reconnect the am10 to the boiler. The c wire connection to the relay is the only question I have . Currently it shares coil #1 with the rh wire to the nest and the W1 wire to the nest is alone on coil #3. 

HomerJSmith

So relay coil 1 has 2 wires connected to it?

Yes, #1 & #3 tabs.

C wire to c terminal on nest and 1 leg of transformer?

Yes, connected to the leg of the transformer that is not going to the Rh terminal.

By program level 5 you mean the outdoor temperature cutoff?

Yes. Blue is fine.

The leg of the transformer that goes to the rh nest terminal also has the c wire on the same coil #1?

Yes, the #1 tab on the relay goes uninterrupted to the leg of the transformer which is not connected to the Rh at the Nest. You mentioned that the transformer leg is connected to the relay #1 tab.

should the c wire to the nest share terminal #3 with the W1 wire?

NO, NO, must be connected to the transformer leg and not thru the coil.

The c wire connection to the relay is the only question I have .

I explained this all in the earlier post.

JJTraxx

I am really trying me best to understand. So the c wire should be spliced into the transformer wire before that transformer wire attaches to the relay.  When I said relay coil #1, I meant tab 1 on on the relay. Not familiar with the terminology. 

HomerJSmith

Yes, normally I would splice the transformer leg to the relay #1 tab along with the blue C wire from the Nest C connector. The relay #3 tab wire goes to the Nest W1 connection.

JJTraxx

JJTraxx

Tabs 2 and 4 on the relay go to tt on am10. 
Tab 1 on the relay goes to 1 leg of transformer 
  Other leg of transformer goes directly to the rh 
  on the nest
Tab 3 on the relay goes directly to W1 on nest

You're telling me to splice the c wire into the relay tab #1 with the 1 leg of the transformer. This would be so much easier on the phone. Lol.  I really am trying. I have zero exposure to schematics and electrical symbols and nomenclature. 

pecmsg

NEST 
is about a Dumb as you can get. I don’t know a worst control you could have chosen! 

JJTraxx

Thanks for the constructive help Pec. 

JJTraxx

Homer...  Got it wired up properly now. Everything is connected and seems to be functioning properly. Nest sees power, relay clicks as call for heat comes and then is satisfied. After testing the boiler from the nest, I tried to turn the temperature up from the nest app and the buderus showed code 0a. 0A – Clocking active: the delay time has elapsed between the burner shutdown and start (service function 2.3b).  I assume it waits a certain amount of time before firing again to avoid damaging the equipment. Thank you so much for your help. It made a huge direct difference to me! You rock! 

HomerJSmith

A word of caution, ONLY use the app that comes from Google Nest. After market apps are problematic. Make sure the app has the Google logo when you load it into your phone. You also need a router connected to the internet, I think.

You may be above warm weather shut down.

JJTraxx

Yep... I am using the nest labs app. Probably going to reset the nest and add it using the Google home app. Thanks again. 

pecmsg

JJTraxx said:

Thanks for the constructive help Pec. 

In my 45 years I’ve never seen as many issues with one t-stat as the NEST. 

Believe all the Google hype you want. 

Do a search on NEST Issues. Just use a non Google search engine’

JJTraxx

Thread closed.