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Munchkin School . . . i.e. can you school me.

Two specific questions. This is a pair of pre Rev. 140Ms that got the 925 upgrade. The manual for 925 style REV 1 shows a specific adjustment for the Dungs gas valve for combustion adjustment, but the earlier manual for the honeywell style offers no procedure for combustion analysis. I have an extra Dungs valve around but its from an 80M and not the same part numbers. (although the blower part numbers between pre Rev and Rev 1 are the same. I'm going to do a test on monday and if its good on CO and rational on CO2 then i'll leave well enough alone. Maybe there is some self evident regulator screw on the honeywell. I'm kind of hoping I don't have to upgrade the gas valve in order to get combustion adjustment although the thing seems to run like a top so maybe i'm worrying about nothing. i'll know monday.

In terms of anticipating headaches I might encounter, I noticed threads expressing preference for the longer post purge on the 926 board. These boilers don't seem to have manifested any noticeable corrosion around gas valve or blower from seeping of combustion products from chamber after cycles but in contemplating parts to keep around, I'm wondering if there is any reason not to keep a 926 on the shelf instead of 925. most function parameters I'm concerned with monitoring seem the same. Since the unit has already been through an upgrade to the 925, it looks as if all the sensors are the same between the 925 and 926 so I wouldn't need the 'kit'. The display board is a different number but the plug looks similar. I'm wondering if I wasn't concerned with accessing new parameters and i'm not using the 'vision' capabilities if the display from the 925 upgrade would be compatible with the 926.

And I may get this by stepping through text mode, but i can't find anywhere in any of the documentation what the target speeds are for various levels of fire and would be handy It does appear that parameter d7 would return the RPMs/10 of the blower but it would be nice to have a theoretical targets to compare just to see if there is any falloff or discrepency and what range around the targets is considered normal - kind of like the target range for recitifcation and ohm range for thermistors provided.

I also don't find much discussion on actual operating theory with regard to choice amongst modulation steps. It would appear that the Rev 1 starts on low and then revs up (sorry), but that might depend on the parameters at start up. And not sure what rate of rise it's looking for to stay at low vs. ramping up. Yesterday I had 'em running and I didn't have the manual so I didn't have the instructions for extracting the fan speed parameter but the lead boiler seemed to run on low virtually the whole day without shutting down, which actually makes sense in that it was maintaining just under the set point and this system has constant demand when the outdoor temp is below 70. The only down side to this, if it was a downside, was that the PC-702 staging these would call the second boiler occasionally as it sometimes didn't see quick enough response from the single boiler. I was wondering if I set a higher differential and target temp maybe the munchkin would ramp up a bit before calling the second one. Obviously, we're in shoulder season. I am expecting both to get called in deep winter and maybe there is nothing wrong with both getting called on low right now but i was just thinking in terms of keeping starts down whether it make more sense to ramp the one running a bit if I could before the second call. The PC-702 is just as much of a black box but I think it gives about 5 minutes to see some unspecified rate of rise before it calls the second boiler so i'm just trying to understand the ROM algorithms of the munchkins a little better so I could use what i know to make the best operating settings.

Any Munchkin afficiandos feel free to pile on. The one call I had with HTP, who were reputed to be right on the money with assistance for munchkins when they came out, the tech seemed less interested in someone who is babying these older units along instead of just migrating to the latest models. I have to say, while I don't mind seeing Heatmakers in the rear view mirror operationally speaking, Heataker tech assistance - even following several acquisitions - was spot-on and I never got the impression they thought we should just throw the things away and buy the new product. Looking these munchkins over, little cleaning and new refactory and they seem to run quietly and effectively and i can't see any reason not to keep 'em chugging (which is what i did with the Heatmakers until the heat exchangers gave out).




  • Tim McElwainTim McElwain Posts: 4,237Member
    Get in touch with me at [email protected] I have re written the manuals on those Munchkins and my manuals answer the questions you are asking.
  • archibald tuttlearchibald tuttle Posts: 614Member
    thanks tim, will do.

    update for anyone following along, of course other jobs have kept me from getting back there (and i haven't had instructions on adjustment of the honeywell valve so haven't tried to adjust them yet, hopefully Tim has got that nailed) but just on an operational flyby check I had the instructions for accessing functions (press and hold button 4 until display changes and then press once to cycle through each parameter) one ramps to 3850 RPM and the other to 4600 at high. don't know if that is indicative of the fan getting old or whether it is normal to have a difference of that range between a couple units. they both start up in the low to mid 2000s which is low middle of range which goes down just below 2000.
  • unclejohnunclejohn Posts: 1,373Member
    You need a 27B stroke 6
  • archibald tuttlearchibald tuttle Posts: 614Member
    i fear i may have tampered with it myself . . . but it was worth it for that great hoskins cameo.

    PS- howse your band (wind it back to the beginning for a great intro)
  • unclejohnunclejohn Posts: 1,373Member
    Thanks I needed a Jerry fix.
  • tc60045tc60045 Posts: 31Member
    My munchkin died of multiple component failure in December. Replaced with two wall-hung Navien NFBs and I am not looking back. Best of luck to you and know there is life beyond...
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