Munchkin Versions and control stategies/blocked vent control/ vision

archibald tuttle

I have a Munchkin in service in a staged setup that replaced a heatmaker. i make it out to be a prerevision munchkin that was upgraded from the honeywell control to the 925 so it is now Rev 1 although i don't believe it started that way. Bought another one to replace the heatmaker it is paired with which seems to have similar vintage and 'upgrade' but does not have a blocked vent control which the first one did. (Having run into 2 like this i don't know if the honeywell panels had a habit of giving out or if people just desired the features of the 925 so they upgraded or . . . ?)

The blocked vent control is not inline to gas valve (Which it is certainly possible i could just add the blocked vent control and make it inline), but both of these units have 925 boards and on the one without the control there are no wires to the pin outs for that control. Since that control has a blocked vent fault how does it operate with nothing on those inputs?

And this is all run primary secondary feeding fan coil units staged by a TACO PC-702 which handles the outdoor setback. So there is no 'Vision' control (i.e. onboard setback) some programmed paradigm is still controlling modulation. I'm getting notable condensing, esp. compared to the non-modulating Heatmaker 9600s i'm replacing. But I can't really find any documentation on how it controls its modulation without a Vision unit. MAybe it watches rate of rise or distance from boiler temp setpoint -- (and predominately i think all the vision unit would do is move the setpoint , i don't know that it alters the modulation regime).

So, anyway, these things are quiet cute, and i'm not sure why the manfacturer moved on other than the constant desire for newer flashier crap.

Any input appreciated.

Brian