Bosch FW 200 on my Greenstar 151 with error 15

condenseit

To do outdoor reset control Bosch told me I needed the FW200, so I got one and put it on the front of my boiler today.
I did not put the Bosch temperature sensor up because my contractor had already put one up, a standard Honeywell 2 terminal deal. The two sensor wires are attached to the A and F terminals on the board in the boiler. I checked the connections, and put my volt meter across the A-F terminals on the boiler's board (power off) and read 1660 Ohms, and it was just over 30 degrees F outside, which seems right.

I am getting error 15: outdoor temperature sensor not connected. Outdoor temperature not available.
Why if the resistance is measuring properly right at the screw terminals on the boiler is this thing (the FW200) not reading outside temperature? Bosch will not talk to me unless I am a contractor. Please help
I can A) get a Bosch temperature sensor and replace my brand new (apparently working) one. I need the part number because the FW200 I bought was used and working, but did not come with the outdoor temperature sensor. I probably don't need the housing just the electrical thermo resistor.
? I don't know what else to do.

The boiler is a brand new Bosch 151 combi boiler installed with baseboard heat in two zones (up and down stairs).
Seems like a great machine.

I want to have the boiler water temperature adjusted based on outside temperature.
I need 175 F water when the temps are -10 F, but can run cooler boiler temps when it is warmer outside.

Also, is the FW200 compatible with my Google NEST?
Also, why is this so complicated??

Ironman

Is it a floor or wall combi?

condenseit

wall combi

GW

Yes I have seen the boiler do weird things after you first start the boiler then you add a “new peripheral “ device. Did you cycle the power off then back on?

You may need to reboot the system, I am sure there are videos on how to reset. You may need to reset the FW200 and it the boiler control. If that doesn’t work, you need Bosch tech, possible a bad control (extremely unusual). I have more buried somewhere in my phone.

Nest——yes and no, most people don’t recommend outdoor reset with a nest. You may wish to turn off the learning function on the nest. Also the nest needs a C wire, no basic common terminal on the Bosch. Do you have a zoning system? If yes that means you should have an easy common (c) terminal to grab. If no you will not be thrilled- need to set up a trans and a relay.

Easy? This trade isn’t for everyone, little technical stuff here and there

Ironman

Ditch the Nest. Their operation is counter productive to the logic of a modulating appliance. You'll use less energy and have better comfort with a standard thermostat left at one temperature.

condenseit

I am looking into ditching the NEST. I want to run a lower boiler temp when possible. The low setbacks I have chosen is causing the return of a good room temperature to take too long, which is uncomfortable.

I actually have two zones: 1 nest on the main floor, and one digital programmable thermostat on the second floor.
I have a Taco SR-502-4 two zone switching relay (a 12"x10" green box) that both thermostat wires go into, then one 3 lead thermostat wire to the boiler.
I am considering selling the NEST and purchasing one Bosch BCC50 or BCC100. I think I have to keep the Taco, because it controls my two 007 circulators.
How do they play nice with my condensing boiler any better that the NEST?

Other option for running an ultra low return temp: quadruple the size of my radiators? haha

EdTheHeaterMan

the problem with all the internet thermostat is that they do to many things they try to be smarter than a regular thermostat. "Adaptive Intelligent Recovery" "Learning Thermostat" if the algorithms are not speaking to each other, then it is like an Asian telling an American how to operate an Italian device. It might get there eventually but a lot is lost in the translation! If a setback is not in the Bosch control logic then don't try to add it with the NEST!

condenseit

So my outdoor temp sensor is indeed a BOSCH
part number 6 720 649 714
http://buderus-pt-pt-b.boschtt-documents.com/download/pdf/file/6720649714.pdf
I think this temp sensor is not exactly the same as the one that comes with the FW200 in the box. However I would be very surprised if this one would not work with the FW200.
Now I am even more curious why I am getting a error 15. I did do a factory reset of the FW200. Still no joy.
I will do another factory reset and completely turn of the breaker on the boiler for a hard set / reboot.

Another question, why would someone have an accessory supply temperature sensor directly mounted adjacent to the boiler supply? I have a two lead wire just laying there without anything to connect to it
I do not have the Bosch CZM100 but the notes on the CZM say that it is not compatible with the FW200. Maybe these both do the "same thing" and try to adjust boiler temperature based on the outside temperature. The interesting thing is that the CZM attaches to the bus connection "B", and not terminals 2 and 4 for "Room thermostat - dry contact"

Ironman

A common misconception is that you can make a system more efficient by adding any or all "energy saving" components available. As stated, that's just not true and the end result is a Frankenstein system.

There are two basic ways to approach reset: either outdoor or indoor. There are also some that do ODR with indoor feedback. The FW 200 is ODR; the BCC 100 is IDR and works very well. I would use that with your boiler and forget about the FW 200 and the Nest.

The nice about IDR is that you don't have to program a reset curve or the like. The controls will figure it out. Just leave them set at one constant temp.

condenseit

thank you everyone. I am commonly misconcepted.
I may call Bosch frontline support and talk to them about brining on a BCC50 for my main downstairs zone. I still have not been able to get the FW200 to see the outside temperature sensor, either by resetting the boiler, powering off the boiler and restarting, or factory resetting the FW200. I don't know what else to try in order to get the FW200 to work.
I have started evening out my programmable thermostats to a "set and forget" single temperature.
I would like more information on if a BCC50 and FW200 do in fact work together, even if the on/off thermostat signal comes in via the Taco equipment. I could be happy with the indoor reset only, especially if it did adjust my boiler to be efficient as possible.

Ironman

I wouldn't trust a used control sold on the Internet.

If you wanna do IDR, then you would discard the FW200 and both of your current thermostats as well as the Taco SR502.

Bosch's IDR system is communicating (not switching) and requires that all components be part of their proprietary system.

You would need the following components:
1. A CRC 100 or CRC 200 thermostat for each zone
2. A CZM 100 zone control
3. The Bosch supply sensor installed just after the p/s Tees as shown in the I/O manual.

GW

Bob the FW200 can be used as a room sensor. It even comes with the plastic housing to do that.

You disconnected the wires at the boiler, and you’re getting the correct ohms? Does not sound good then.

Always lots of ways to do this. If you install the control in the living space,
You could wire the “main zone” to the boiler’s pump output and the leave the taco for the second zone.
You could wire the pump output on the boiler to activate both zones with the ZC terminal (simply jump the low voltage TT terms), and not use either old stat

Probably more a way to do this also. Your boiler is quite large, is your house very big? Having zones is wonderful but the large boiler will cycle badly.

Ironman

Gary, that's true, but why invest any more effort in a control that was purchased used and now appears to be defective?

I agree about the over-sized boiler. Quite common when a combi is chosen.

@condenseit
You may be better off combining both zones and using one CRC 100 or CRC 200 thermostat. That would help prevent short cycling. Then you would not need the CZM zone control. As Gary mentioned, you could use the "CH" terminal in the boiler to power the "ZC" in the Taco. Wire the CRC thermostat directly to the boiler's "Bus" terminals and jumper both "R&W" terminals on the Taco.

condenseit

I just took the outside temperature sensor off the building and brought it inside to test in isolation. Thanks Gary.
The sensor on its own not connected to any wires was reading 22 kOhm resistance at 40F, 17 kOhm at 50F, I also breathed on it and it got down to 7 kOhm.
While I had the boiler power unplugged I checked the resistance across the A and F terminals, where I got 1.688 kOhms as I reported earlier, so my meter was reading that resistance then as now, as I had left the wires to the sensor attached (my error thank you again Gary). This 1.688kΩ value is without the FW200 attached.
These isolated sensor resistance values seem much too high as my Bosch Greenstar 151 ZWB42-3A manual (page 59) says they should be:
-4F =2.392 Ohms.
10F=1.811 Ohms
32F=1.149 Ohms
50F=781 Ohms
not KiloOhms (kΩ) but Ohms (single capital Omega Ω) and so on from Table 16.4.1
Weird that not all Bosch temperature sensors are the same?
Is the proper accessory outside temperature sensor for the FW200 that different from the Bosch outdoor temperature sensor unit my contractor installed?
My house is 1600 sf, two floors and built in 1900 with whatever that has for insulation, but has had blown-in insulation in the attic floor and has vinyl windows and siding with 1/4" insulation under the siding. I had hoped to get the 131 boiler because it is smaller and quieter but my contractor insisted I needed the bigger boiler running baseboard.

GW

I don’t know, the more hands that touch a system the more possibility of something going astray (during the installation process). If you’re ohming correctly then perhaps the sensor is bad.

True, some sensors have the same resistance yet others will be different. I don’t have enough sensor issues to necessitate memorizing which ones are similar resistance. Some simple things I can remember, like a Viessmann tank sensor is the same as a Viessmann low loss header sensor.

Large combination boiler is good for Domestic Hot Water but not super good for space heating. If you have cash on the money tree you might be well served with a buffer tank. That would reduce boiler cycling. It simply adds mass to the system. I’m a tank guy, don’t really dig the combination boilers. I’d rather waste a few bucks in fuel (tank losses) than lunch a boiler every 8 years.

And-or, if you’re extra nerdy, make your home a one zone system in fall and spring and perhaps go back to two zones in mid winter months. No normal person does this, but you seem to appreciate the “next level” of how these systems really work.

condenseit

I could make it one zone with the wiring inside the Taco I suppose. And switch it back to two zone in the dead of winter.

Is ODR an "old technology" whereas IDR is "newer"? I had hoped running an ODR would lower my boiler temp and reduce short cycling by putting the boiler more often into low-fire mode. Perhaps IDR is better for reducing short cycling because it keeps track of cycle times and is supposed to adjust boiler temps to improve cycle time, something an ODR does not consider. Not sure if this is factored in but a wifi thermostat should be able to get local outside temperature from the internet as well. My situation maybe would be best served by a CMZ100 and CRC 100 or 200s for my 2 zones. IDR.

Thank you all (ironman GW and Ed especially) for taking the time to help me learn more. This is a starter home and perhaps I should have done more research before agreeing to the current install. Hopefully in 4-7 years I will buy a new house and build a perfect heating system the right way in my forever home :0
This new hot water system is a step up from the 1994 steam boiler that was heating the house (along with the rented 40 gallon hot water heater) in every way for me now and the next owner.
Until I get to the CMZ and 2 CRCs (I would rather use a BCC and my FW200 as my in room thermostats), I will be making a new post looking for more information on the outdoor reset sensor, and trying to get the FW200 (on the boiler) to do ODR while keeping my "smart" thermostats at more or less set temperatures without large set-backs.

GW

Both are good, neither is old. With idr how do the “other zones” heat effectively? I haven’t had any good vibes from IDR, I’ll stick to outdoor reset

If it’s radiant or cast iron I want both: outdoor reset and I indoor sensing, anything else don’t really care as much. You gotta burn fuel to heat the home no matter how you slice it

condenseit

The sensor my contractor installed is 10K at 77 degrees F for Buderus boilers and controls. Hexagon enclosure

The temperature sensor I need for my used FW200 is a 4K sensor part number 87472071010. House shaped enclosure.
Hopefully the used FW200 works ok with the proper temperature sensor.

This has been a rollercoaster ride with all the advice I am getting, which I asked for and I feel like I should know these things no matter how hard they are to hear.
I am hoping to improve my situation slightly with the ODR. But likely #1 my boiler is oversized, leading to short-cycling and decreased longevity, although I do have great DHW supply. #2 my radiators are undersized leading to lower efficiency as my supply temps need to be at the high end (unto 180F), which prevents me from attaining a nice low return temperature to properly gain my efficiency boost from the condensing boiler. #3 my Nest is not playing nice with the condensing boiler because of the large set-backs I was programming, and I should leave my home at more or less a uniform temperature especially if the ORC runs lower boiler temps. #4 The Bosch-Taco-Nest setup is like speaking German-Spanish-Martian and wanting good communications. I maybe should have gone with all Bosch controls and maybe I will unify those, although I will have to ditch the FW200 if I bring on the CMZ100/CRC100.
Getting the proper temperature sensor will at least allow me to run the outdoor temperature adjusted boiler temps, which will let the boiler kick into low-fire at temperatures where condensing mode is happening more often, and using less of the NEST automatic settings will let the boiler be more in control.

I am planning to put 2' of 4" clamp on radiator fins around the 1-1/4" return line close to the boiler to further lower return temps (and to get some heat in my basement). I can add a thermo switch at 120F/on 110F/off and a fan to keep condensing!
Thank you.

GW

Yes it’s not cake, keep chipping at it