Buderus GB142-24 not producing heat

kerd

I have a Buderus Logamax Plus GB142-24 that will not produce heat. I first noticed this morning, but it's probably been like this for a day or two. Initial observation is that a few rooms in the house seemed a bit cold (we have radiant heating).

I'm comfortable with DIY stuff, but I would normally call a service tech since this is a gas appliance – happy to trade dollars when there's risk involved. Of course, everything is different with covid in the mix. I would like to eliminate any obvious and/or easy fixes myself before calling someone, so I would appreciate any suggestions / next steps.

Things I've done / tried:

• turn it off/on – no change at startup, went straight to ~82F and didn't light the pilot, no error codes
  
• empty out condensate trap – last emptied ~11 months ago, had some accumulation this time but didn't seem excessive
  
• adjusted temperature for DHW – turned down to "Eco" (lowest setting between "0" and "90") from starting position of ~120F. Within a few seconds of doing this, the boiler fired up, lit the pilot, and temperature on console showed 120F and climbing. It turned out this was temporary – I walked away, and returned 10 minutes later find the boiler again sitting idle, temperature display showing ~80F like before.
  
• adjusted temperature for heater water – tried various values, no observeable change
  
• check diagnostics – console shows "0Y" which the manual says "flow temperature higher than set" without further detail. No error codes. This shows that the boiler thinks things are fine, normal operation, no issues.
  
• called Bosch support – they wouldn't tell me anything without a licensed tech standing next to me, even though I explained that's the very point I'm trying to avoid.
  
• verified that inlet and outlet are both clear, unobstructed at the exterior of the home
  

I found a bit more info about 0Y, outside of the operating manual. This is a generic list of Buderus error codes (not model specific, which may or may not matter) https://helpdeskminority.com/buderus-gas-boiler-error-codes/ which has three entries for 0Y (listed below). From the manual's terse "flow temperature higher than set", it seems like this could easily be a bad sensor, but I'm not sure which to look at, or how to verify. Sensor replacement looks straight forward, not related to gas, just shut off the unit. Anyway, I think that's all of the info I've got. Thanks in advance for any help.

0Y – The actual flow temperature is higher than the set temperature. The boiler switches off.

0Y – The temperature at the flow sensor is more than 95 ° C.
This message may appear in the absence of a malfunction if all valves on the radiators are suddenly closed or after the hot water is removed from the GB072-24K.
Check the working pressure in the heating system. Open the service valves.
the heating circuit pump Electrical connection to the main controller BC20.
Rotate or replace the heating circuit pump.
Correctly set the power of the pump or its characteristic and reconcile with maximum power.
Check for damaged or short circuit to the flow temp. sensor, replace if necessary.

0Y – High temperature on the hot water temperature sensor
Check the correct position of the sensor.
Check it, and if it is defective, replace
Insert the KIM correctly, replace if necessary.

EDIT: added another thing that I checked earlier, but hadn't included in the list: verified that inlet and outlet are both clear, unobstructed at the exterior of the home)

Jamie Hall

Well, at least the descriptions are more or less consistent on the underlying symptom, if not the cause: the boiler thinks the flow temperature is higher than the set temperature. However... i this isn't real (likely not, since it just won't fire!), it could be the sensor itself is defective. It could be a loose connection or a problem with the wiring from the sensor to the control board. It could be the control board has lost its mind.

It almost looks, sadly, as though -- like so many modern things -- this may be an exercise in parts swapping for much money, unless you can find the specs on the flow sensor itself (likely a thermistor) and determine whether or not it is behaving properly.

HVACNUT

That code wasn't there before you changed the settings, correct?
Put the settings back where they were.
Is there an indirect water heater piped and wired to the boiler? If yes, do you have hot water?
How many thermostats are there? Is there a zone panel?
It might not be the boiler but a zone control. 

Zman

That model is not particularly friendly to the DIY tech.
I would start by jumping the TT wires coming from the zone controls to be sure the boiler is actually getting a call for heat. Beyond that, the service manual has tons of logic diagrams to help troubleshoot you can take a look at, but it might be best left to a qualified tech.
Post pictures of the controls wiring if you are unsure how to jump the call for heat.

kerd

thanks for the replies.

it could be the sensor itself is defective. It could be a loose connection or a problem with the wiring from the sensor to the control board. It could be the control board has lost its mind.

Those all sound plausible. I could see blindly replacing some sensors (like both supply+return NTC sensors @ $83 each, maybe the safety high limit sensor for $143), seems easy enough to just power the unit down and swap them out. But as you pointed out, it could be a number of other things and maybe I'm just wasting my time+money. Overall, it seems like this is the one step I might take (swapping those sensors) before calling someone in.

That code wasn't there before you changed the settings, correct?
Put the settings back where they were.

The code was there before I made changes to either temperature. I have since tried putting both temperatures to "auto" which resulted in the boiler firing up after a few seconds, and steadily increasing temperature (on console screen) to 181F over the course of ~8-10 minutes before it shut off and quickly descended back to ~80F. If I were put both temperatures back to where they were, what would I be looking for at that point?

Is there an indirect water heater piped and wired to the boiler? If yes, do you have hot water?

We have a Triangle Tube Smart 50, Phase III, and – for now – yes we do have hot water, but I'm not sure if that's "new" hot water, or what's been sitting in the tank but hasn't gotten cold yet. Is there a way to tell? I guess I could just run the tap for a while and see if it gets cold?

How many thermostats are there? Is there a zone panel?
It might not be the boiler but a zone control.

I'm not in front to count but there are at least 11 thermostats, and three separate zone valve control boxes. The lights on each box look identical – an orange light lit next to each "thermostat", and a red light lit next to each "zone valve". I don't have verification/proof, but I'm pretty sure it's always displayed the same orange+red lights (even when things are functioning normally).

That model is not particularly friendly to the DIY tech.

wheeeeee 🎉 I'm comfortable figuring things out, even when well out of my comfort zone, but not sure how to best navigate the risk/reward combo working on a gas boiler vs. unnecessarily exposing my household to covid risks. So it's helpful to hear this perspective. Appreciated.

Big Ed_4

Check the outdoor sensor . What temperature is it reading ? Is it close to what is ?

Zman

Are you handy with an electrical multimeter?
You can check the resistance on all those sensors without replacing them. The service manual will have the specs.

kerd

The last change I made was to set both temperature controls to “auto” (where DHW had been ~120F and heater water had been ~140F prior). I did this around 2pm today. No changes since.

After leaving the system for the second half of the day (~8 hours), here’s what I’ve observed:

• Boiler has turned on at least a few times, observed it at 100F and pilot on earlier this evening. Seems to be working fine.
• One of the rooms that was initially a signal of heating issue - showing 67F on thermostat and felt cold - that room is now up 2F to 69F.
• Most other rooms are not showing any changes in local temperature, they seem to be holding temp as expected.
• Of the three zones, one of them has the formerly 67F room. Another zone has a separate area that has seemed cold for a few days, and the third zone has no obvious temperature issues.
• Faucets throughout the home are plenty hot.

Is there any chance that a sludgy condensate trap would have been a factor? And that emptying + cleaning it would have affected anything in a positive way? It seems like the answer should be “no”, but I’m just calling it out since it’s the one other thing I did (besides changing temp settings).

I don’t know the root cause, or what the trigger would have been, but for sure it seems like this isn’t an issue with the boiler.

Ironman

It sounds like you’re not getting circulation during space heating. Check the boiler and system pumps.

subcooler_65

If the boiler temp ran up to 180* its trying to satisfy the hot water demand. It wont heat the house until the H/W is satisfied. Probably have a bad circulator pump. Turn the H/W temp control all the way down and see if the heat comes on.

kerd

We’re just about a week after the initial issue last Monday. I haven’t changed anything since then, settings are still at “auto”. The rooms which had been cold before are no longer cold – temps around 70 or 72 on thermostat. Hot water at the taps is definitely noticeably hotter than before, but otherwise things seem stable.

Are there any good troubleshooting steps for a bad circulator pump? How long do those last in general? We’ve been in the home for 3.5 years, so they’re at least that old.

Looking at our setup, we have three zones, one per level of the home. The boiler and hot water heater are on the lower level, and the “cold” room is at the top. There are two pumps – it looks like one is for the lower level / one, and the other for the upper two levels / zones. It would seem like that second pump would have more work to do over time, dealing with higher elevation and more overall distance.

Is a pump replacement simple? It looks like these pumps are both bolted inline, such that I would remove bolts and the pump would come out. I’m probably missing various important details but it looks like I could drain the water, remove old pump, insert new pump, and have it over with. Too simple?

Big Ed_4

On the AM10 control what is the outdoor temperature reading ?

kerd

Big Ed_4 said:

On the AM10 control what is the outdoor temperature reading ?

It varies through the day, but it’s currently showing 28F which is close to current actual outside air temp.

kerd

Things seem to still be working, although I don’t have an explanation for what changed to cause the initial issue a few weeks back. I guess that’s good (?).

I found a book - Hydronic Radiant Heating by Dan Holohan - that might help fill in my understanding of the system, how things work, and maybe shed some light on what went wrong (or maybe clues to find if something’s failing).

MeToo

Did you find a fix for your problem? I am having the same problem.

Big Ed_4

Was it the set back program with the wrong time ?