Buderus GB 142 - 2F

kinderhund

Seems every time it gets cold, we get an error code! And the heat isn't really the issue for us. The lack of hot water tends to make people cranky.....

So getting a 2F code. I saw a video indicating that the resistance on the 3 sensors (safety, supply and return), should all be within 10% of each other, since they should all be reading the same temperature. Can someone confirm if that's correct?
On mine, I got readings of 4700 and 4800 ohms on the safety and supply sensors, but 6000 ohms on the return sensor, which suggests its gone bad. I don't have my temp gun here (its out of town for a few days), but I did use a digital food thermometer and got similar temp readings at each sensor location...

Agree? Bad sensor?

mikeapolis

Bosch has excellent tech support. If you haven't already contacted them, I'd recommend giving them a call:
Tel: (603)-552-1100 Toll Free: 1-800-BUDERUS

Here's a link to the manual(Page 49 for your 2F Code):
https://s3.amazonaws.com/s3.supplyhouse.com/product_files/Buderus - GB142-30 - Service Manual.pdf

Page 91 shows how to replace those sensors

Big Ed_4

If the boiler is off on error the temperature should be the same . You can just feel the locations to see if they are close . I would replace all three sensors , the good ones keep as spares ..

kinderhund

Update - replaced the sensor, now getting similar resistance across all 3 sensors. Still getting 2F error though, which according to the manual now indicates primary circulation pump. Going to see if I can hear it spin up on startup. Any other way to know if it's operating?

Ironman

Is there any temperature difference between supply and return?

It could also be air bound.

mikeapolis

What kind of circulator is it? If it's not an ecm circulator, you can use a Grundfos Run Indicator Magnetic Rotation Key. I agree with Ironman that it could be air bound.

Ironman

It’s usually a Grundfos 15-42 or 15-58.

Big Ed_4

Top left on heat exchanger is where the float vent is installed to remove air. Its easy to replace... Just make sure you hang the float like the one you pull out ..

kinderhund

Update: I did my best to remove air. Still nothing. Called in a tech to have a look, and they got Buderus on the phone as well. Did a proper flush of the system, refilled and purged. Still getting 2F code.
According to Buderus, the issue is actually the control board - there's some kind of short between the unit calling for heat for hot water, and firing the boiler. Because it prioritizes hot water, it won't fire for floor heating either. By setting the water temp to zero, we can at least heat the floor while I source a new control board.

mikeapolis

Good luck. Hopefully, that board will take care of the issue.

kinderhund

So the control board is a 2-3 week delivery. While I'm waiting, here's a question for the electrically-minded (see photo)


The image shows the control board. On mine. RC and FA aren't used. WA is the hot water signal, and FW is the floor heat signal.

PK is used for both the primary circulation pump, AND the floor heat pump (from what I can see), and PS is used for the hot water tank pump.

The control panel recognizes we need water heat, but somewhere between there, WA and the boiler/pump, the signal gets lost. Hence the new board.

Here's the question - since I already have 2 pumps connected to PK, what would happen if I connected the hot water tank circ pump as well? The heating water would move through that coil as well as the floor coils, but only when the floor was calling for heat. But in theory that might keep the water warmer than it currently is, for slightly less painful showers. Thoughts?

EBEBRATT-Ed

Probably would work but I would hate to see you cause any damage if the xtra pump overloaded the circuit or relay contacts.

Why not disconnect the pump for the water heater and hook it up to an outlet with a cut off extension cord temporarly of course

1der

Our 2F code was created by the temperature sensor in our AMTROL 75Gal Hot Water DHW Storage Tank.

We had DHW but no radiant floor heating. Test condition was to turn down the DHW temperature dial to 90F to see if the Floor Circuit would stay lit with demand. It did.

Our tech suggested checking the temperature probe that runs up the middle of the 14 yr old tank. The probe had slipped all the way down to the bottom with a large loop of wire hanging down. What happens is the probe never senses the DHW tank reaching temperature because it is near the bottom of the tank in near ambient air. DHW demand is primary to Floor heating circuit, so, the boiler was always trying to satisfy the DHW demand and never being freed up to satisfy the floor heating demand.

The 2F code was seeing a larger delta between the three sensors indicating a larger than allowed difference so it was shutting the system down when the delta was exceeded.

We pushed the probe back up into the probe cavity and wedged the wire so it would not fall down again. All started working as designed.

Thankfully an easy fix with guidance from our local tech.