Buderus GB142/24

ToddM

I have a gb142 at a customers home that will not run. It was not serviced in the last year and a half (I did and now its clean inside) It was showing a 4P code  interrupted safety sensor. I followed the service manual and changed the sensor. Woo hoo it runs-but only for a cycle long enough to make hot water. Then it shows a 4Y-interrupted supply/return sensor. I call the factory. I go thru ohming out the sensor cables. they check out fine. Factory says new UBA-ouch ok I find on and replace that last night still getting 4Y and 4P codes. call factory again. now they say to replace low voltage wiring harness. But I tested that before and it checks out. This unit was installed 10/09 by a different contractor who neglected to inform the customer that these boilers need YEARLY servicing. Anybody out there have any ideas?

STEVEusaPA

Odd.

This may sound rhetorical, does the whole system, especially around the control and wiring harness seem to be running hot before lock out?  Are you checking the sensors cables right when the system locks out?  Besides checking the incoming voltage, hz, and cycles, at the panel, and coming into the control, which, if too far from a normal range, could be locking out (fooling the control), I can't think of any other options besides changing out the whole control (yikes).  Please post back your results after it's working again, because this is one of those service calls most of us will encounter with frustration.

Ironman

Have You...

Checked the supply sensor to see if it reads the correct resistance at the corresponding temp?. It's a 10K ohm thermistor, which is the resistance it should read @ 77*.





P.S. Just read your post again and saw that you had replaced the sensor. In that case, the wiring harness is the next step. It could be it's not making good contact in the connectors.

meplumber

Ok this is gonna sound weird.

When you serviced the boiler, did you happen to clean out the condensate trap? 



The aluminum block is reacting with the chlorides from the pvc venting (or some scientific crap like that) and creating a gray mush.  When the condensate is unable to drain from the block, it usually spits out a 6P error code, but I have seen it spit out a 4P once.



Take a look.  Run your finger up into the block where the condensate trap attaches.  Make sure it is clear.



Good Luck.  Let us know what the resolution is, so we can add it to our own book of tricks. 

ToddM

still acting up?

So I spoke with the Buderus rep this morning and the first thing he asked me was "was there black crud on the sensors when you pulled them?" YUP. The guy who installed this boiler, installed it on a system that is 18 to 20 yrs old and never cleaned the system. So he recommended doing that. He also said they had one of these that was "driving them nuts" and it ended up being a broken wire in the low voltage harness that was acting up when it felt like it. Right now the inhibitor is rat racing around the system doing its thing. The old sensors both checked out fine as to 10k = 70 degrees as one of you asked. Tune in tomorrow for an update or look over the skies of New England for a mushroom cloud when I shoot this boiler......

Mad Dog_2

Feel your pain Todd

Chuck Shaw @ Buderus knows the product well, did you speak to him yet?  Mad Dog

tim smith

Oh this sounds too familiar

I may be thinking that the broken harness wire could have been one of the jobs my tech was on. I will look up the file on this and see what I can find when I get to office.

ToddM

FIXED!!!!

SO I flushed the system and added inhibitor. ph is correct. inside of unit is clean (no more mush) cleaned black stuff off of old sensors and ohm'd them out (ok) Tried it and ....NO. Changed low voltage harness and yes that did the trick. No new UBA-3,or sensors. Did have to change the DHW sensor tho. It was attsched to the Domestic hot water pipe coming out of the smart tank with 2 cable ties and a hockey sock wrapped around it for insulation (I guess). So I put the probe in the smart tank well and now all is good. Thanks to all for help. 

ToddM

oops