Vision 1 intermittent fault

Tom Hopkins

Jamie_5

I am helping a friend on a T-50 Munchkin (with Vision 1) which has an intermittent problem with hot water production. After watching the boiler a while yesterday, the problem seems to be in the Munchkin electronics.

During the DHW call, the indirect circulator stopped working, causing the boiler to stop firing soon thereafter, since it quickly reached high limit. Checking voltage to the pump revealed 120V between one line and ground, about 50V line to line, and about 28V from the other line to ground. Disconnecting the leads from the pump did not change the readings. Performing continuity and resistance checks on the leads back to the Munchkin board revealed no loose connections between the pump and the plastic push-on connector on the Munchkin board. The status menu for indirect circulator shows "1," i.e. the pump is supposed to be on. The indirect thermistor seems to be working perfectly.

We we were able to the get the fault twice, with the same behavior both times. Is it possible to go further in diagnosing this problem, or do we have to replace the Muchkin control board?

Thanks for any help you can provide.