Munchkin F00 Error Message

Alan (California Radiant) Forbes

I've been serving Munchkins for awhile now, but this was a new one. 



"No Heat" call from a new customer.  F00 error message which translates to "high limit exceeded".  This error message persists after the 925 controller is reset and when the boiler is cold.



HTP tech. support tells me to remove the T-T connection to the boiler at which time the boiler comes on.  He says the problem is not with the Munchkin, but with either the zone valve controller (Taco ZVC 404) or zone valves (Taco ESP or EBV style) which makes total sense.  Turns out the owner has been having problems with the zone valves.



So, what is it in a zone valve or controller that would make a Munchkin 925 controller come up with an error message?  The Munckin sends out one leg of 24 volts to a pair of isolated contacts that close on a call for heat.  What goes wrong?

eluv8

crazy question

If you do not have the T-T terminal jumpered, What is telling the boiler to turn on? Just curious.

Alan (California Radiant) Forbes

The Indirect

There is an indirected connected to the system and as soon as the T-T leads were disconnected, it started making DHW.

eluv8

indirect connected

Ok, that makes a little more sense.



Did you try jumpering the T-T terminal with a wire, bypassing the zone controls altogether right at the boiler?



What does the boiler do if you jumper out the high limit?



Something seems amiss like you said, and usually based on my experience with Munchkin, when everything else checks out it ends up being the control board or corroded/loose wiring from previous service.





 

Jr_12

F00

F00's are often caused by either reverse polarity or "bleeding" of the low voltage which causes the boiler to go into a safety mode and shut down.

If you would have pulled TT and the unit still sat on F00, I would have you jump out the "safety's" until the problem is resolved

Alan (California Radiant) Forbes

F00 Fighters

I didn't try to jump T-T, but I did jump the high limit and still got the error message.



The boiler is a few years old, so I don't think the problem is with polarity, but bleeding voltage may be happening.  If the Munchkin is able to "see" a different voltage coming back when the end switch closes, it may be the cause.

Mark Eatherton

F007 Jet Fighter...

Just kidding, but got your attention :-)



The ONLY 00 lockout I experienced required a re-programming of the mutha board to get the situmucation resolved.



But your situmucation could be different.



ME

Jim Pompetti

First

ohm out each high limit . Sometimes the resistance is to high . 

Jim Pompetti

First

ohm out each high limit . Sometimes the resistance is to high . 

Jim Pompetti

First

ohm out each high limit . Sometimes the resistance is to high . 

eluv8

What he said

JR explained exactly what I have seen. If jumping The T-T right at the boiler with a wire does not correct, my experience was a new board fixed the problem.