Buderus Logamatic: house overheating w/ random DHW PROD ERROR

leeVT

New here and need help! I have a buderus G124 w/ Logalux water heater and Logamatic 2107 controls. I live in rural southern VT and have yet to find a contractor knowledgable or willing to work with the Logamatic, so doing the majority of my own troubleshooting. They all say to get rid of it, but money is too tight to do that right now.

I'm running in Automatic mode. DHW PROD error pops up about once a week at random - I figure it out when the house overheats. It gets 70+ inside but thermostats are set at 60. I suspect if I wasn't home it would continue to overheat. For context we're mid winter here so this is a waste of propane.

I've noticed that when DHW Prod Errors, the mix temp to the ciruclator pumps reads at 135-140F (can verify this is accurate, the pipes are hot), and DHW is at about 120F despite being set at 130F (wife likes hot showers).

It feels to me like the circulator pumps get locked in running mode and circulate the 140ish degree water instead of going to DHW. This corrects itself if I restart the machine, and everything runs as normal until this happens again about a week later. Any insight here? Would running in Manual mode solve anything? Thanks in advance.

Jamie Hall

This is a guess -- but it almost sounds as though there is a problem in the control with a relay (and I'm not even sure there is one, but...) which is supposed to switch from the circulators for the heat to DHW priority getting stuck. Relays do that. Try this (I know it sounds bizarre, but it's an old country trick): when you find the system misbehaving again, try giving the control a sharp whack and see what happens...

Big Ed_4

What is the reading of hot water production showing on the screen ? You may have to turn the knob . Checking the indirect sensor ....

Big Ed_4

The control locks into a default manual mode when it runs too long trying to build up the water tank . Yes, the 2107 normaly control the indirects circulator .

Jamie Hall

duplicate post -- @Erin Holohan Haskell can you merge?

leeVT

hey @Big Ed_4 it reads around 120f when it's erroring. setting is 130f. I keep the knob on AUT, internal thermostat at 160f.

leeVT

sorry folks! i thought I'd posted it (and here it is) but it said I had to choose a category and then didn't see it in my post history.

@Big Ed_4 makes sense that it defaults to manual. @Jamie Hall I'll give it a whack when it happens in 4-7 days and let you know. your tagline says caretaker of museum in new england, anywhere near halifax vt/colrain mass?

Jamie Hall

northwestern Connecticut

leeVT

dang, too far.

HVACNUT

If you put it to manual, lower the left dial to 140° because that's the operating control and will now be the indirect tank temperature. So be careful. 

Ohm out the tank sensor. 
Check amps on the indirect circulator. Is the indirect loop air locked?
Is there freeze protection or circulator exercising? If the indirect isn't heating properly, it might "time out" on priority and switch to the above functions, causing the space to over heat.

leeVT

@HVACNUT thank you. This goes over my head a bit, but if air locked refers to air trapped in the indirect circ pump, that may make sense. contractors have said they purged a lot of air from the system (last owner left nonfunctioning expansion tank on for unknown long period of time). thank you thank you - wish you lived close so I could hire you.

Erin Holohan Haskell

Jamie Hall said:

duplicate post -- @Erin Holohan Haskell can you merge?

I've merged the duplicate posts. Thanks!

HVACNUT

leeVT said:

@HVACNUT thank you. This goes over my head a bit, but if air locked refers to air trapped in the indirect circ pump, that may make sense. contractors have said they purged a lot of air from the system (last owner left nonfunctioning expansion tank on for unknown long period of time). thank you thank you - wish you lived close so I could hire you.

Post some pics of the overall area. Maybe we can walk you through it. If its air locked only, it's not a hard fix.
Any antifreeze in the system? That might be a roadblock to DIY.

leeVT

@HVACNUT worth the shot - posted some general pics below - first few orient to the space, last couple just DHW tank. let me know if you need something more specific. There's an accidental amount of antifreeze one of the contractors accidentally let in - he turned on a zone that's shut down. Not sure how long he'd done that before I caught it. Thank you for this help.

Big Ed_4

You need to check the voltage to the indirects circulator at the time of error . With Voltage circulation problem , no voltage control ...

leeVT

@Big Ed_4 I don't have a multimeter, but it errored this morning and the circ pump connecting the DHW tank to the house was running. DHW pump itsef, supply and return pipes were hot.

@Jamie Hall I smacked the controls, didn't fix anything.

I've boiled this down to happening in the mornings when automatic setting turns from day to night mode. The hot water doesn't heat quickly enough and it errors. It's errored the last 2 mornings, and hot water stalled at 118-120F, but boiler was at 140F and mix temps just under that, all circulators running w/ hot water. Not sure why it's happening more often now. Maybe I just didn't it before and it corrects itself at some point during the day....?

Would putting the thing in manual fix it? Maybe I could manipulate the programmed settings to never shut down DHW production. Would rather fix the actual problem, though.

BPR2107

There are a couple of things you can look at. I have the same Logamatic 2107 control and also at Taco 6 zone SR 506 to control the circulators for the various zones, and indirect Superstore tank for HW. The Logamatic can be wired to shutdown the circulators when domestic hot water is required, but it is not necessary. They do this in Germany (where the unit is from) since they circulate the water all the time and the boiler fluctuates temperate depending on demand and outside air temperature. If the during DW production, the circulators kept running it would over heat their homes. In the USA it is typically used differently: Circulators on thermostats, so as long as the boiler has enough BTUs, DW and heating can run concurrently. (This is how mine is configured). If you have a Taco box, or another, their are specific wiring diagrams you can download to check if it is wired correctly.

The following is from the 2107 manual and may help.

TROUBLESHOOTING A “NO DHW” CALL:

A “DHW PROD ERR” message will appear on the LCD screen of the R2107 control with regard to domestic hot water production.

DHW ERR - when the tank temperature drops to the low limit (9°F below the set point), the R2107 goes into DHW priority mode.

During DHW priority, the R2107 raises the boiler water temperature to it’s high limit, interrupts power to the space heating circuit {terminals 61(N) & 63 (H)} and energizes the DHW pump circuit {terminals 24 (N) & 25 (H)}. The pump circuit symbol is displayed on the LCD screen.

In DHW priority, if the R2107 does not sense a rise in DHW temperature in 30 minutes, it will display a DHW PROD ERR message.

At this point, the control will go back to space heating mode and lock out the DHW to avoid freezing the building. This message is general in nature and the R2107 control is essentially telling you, “I tried to make domestic hot water but nothing happened”.

IN MOST CASES THE PROBLEM IS NOT WITH THE R2107 CONTROL. To rule out the R2107, turn power off to the R2107 to reset. The R2107 will again try to make DHW. Check terminals 24 & 25 for 120V. If power is present and boiler fires the R2107 is o.k.
Check the following:
1 - bad circulator
2 - stuck flow check
3 - piping is air bound
4 - closed valve

Big Ed_4

My first thoughts ,Your heat exchanger in the indirect seems to need a rinsing . I believe there is an access plate on the 40 gallon .Taking too long to recover . ..

Yes , set it to maintain hw for now ...

Looks like the 1" boiler supply was reduced to 3/4" ??

pedmec

Your boiler loop to your indirect is overhead which can be a great place to trap air. If you're positive that the circulator is running try purging just the indirect loop again.

leeVT

@Big Ed_4 that was it! I descaled the heat exchanger and no issues in a week. Thank you sir!