Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Honeywell MCBA troubles?

Pj_5 Member Posts: 6
Hey guys, wondering if any other heating professionals are experiencing a rash of E-12 error codes on TT boilers?

Thanks in advance.



  • tim smith
    tim smith Member Posts: 2,454
    Re: E12 on mcba

    Are you using an indirect water heater with a standard aquastat on water heater. This has been a common problem on Triangle. If so change out to tank sensor and this should end your problems. The contacts on the aquastat have a bit too much resistance for the low voltage traveling on the indirect circuit from mcba. The thermistor virtually has no resistance so you don't give bad signal to mcba then. Good luck.
  • croydoncorgi
    croydoncorgi Member Posts: 83
    Variation between MCBA implementations

    Interestingly (??), MCBAs used on different boilers have VERY different coding in this area.  Some will easily accept a stat OR a sensor.  On this type, if the stat has dirty contacts and present (intermittent) high resistance when closed, it CAN cause over-hot water now and then (is that what  E-12 means on the TT boiler??).

    But on some others (eg. Hoval in Europe), there is specific coding to determine whether a sensor or stat is connected.  If it sees 'resistance' as opposed to open or short-circuit (stat open / stat closed), the MCBA  then assumes that a sensor has been fitted and then STORES this info and requires a manufacturer-only access code to change the  internal parameter back to 'stat connected'.  Until this is done, the boiler shows a code indicating 'wiring fault' and will not work at all!  How dumb is that??
  • Pj_5
    Pj_5 Member Posts: 6
    MCBA & Battery backups

    Here is a good one. The MCBA control used on the TT is not compatible with a battery backup (similar to the ones used on computers). The interruption of the house power (even a few seconds) while having the boiler plugged into one of the APC devices causes the the boiler into a hard lock out E-12. We have used the APC battery backups on other brands of mod/cons with good results, typically to help "clean up" some of the dirty power that we have around here from time to time.

    Oh well, just trying to do the best installs we can and then get bit.

  • HFischer
    HFischer Member Posts: 1
    E-12 from Aquastat

    I can confirm that an aquastat can cause E-12 hard lockouts with an MCBA. We have a Weil-McLain Ultra 80 propane fired at a remote cabin run off generator. For five years it has been stable, despite very dirty power supply. Recently we got a series of E-12 hard lockouts. I traced it back to the aquastat we added two years ago to control a copper heat loop in a hot tub. Seems that the aquastat has been outdoors long enough that the contacts are a bit corroded and that was the cause of the problem. **** that circuit down and the boiler runs fine with no E-12 lockouts
  • SWEI
    SWEI Member Posts: 7,356
    battery backups

    Low priced backup systems have THD issues in their output waveforms. 

    They do not "clean up" AC power any more than so-called noise

    suppressing surge strips do.  The  design increases the effective source

    impedance seen by the load, exacerbating any weaknesses in the power supply input section design.  A few minutes with a scope and some cheap computer UPSes will demonstrate this quite clearly.

    In order to actually filter the noise out of AC power, you need inductors and capacitors sized to the frequency and current involved (translation: big hunks of iron and copper for a 50/60 Hz AC branch circuit.)  If the appliance manufacturer includes this, it can be sized to the susceptible load and will cost far less.
This discussion has been closed.