tk Jr. runs only with cover off

My takagi Tk jr. will only run with the cover loose or off. IT's 6 years old & worked fine until I removed the cover to change an "O" ring in the water control valve. If I try to run it with the cover on it trips out. Any ideas or solutions appreciated. thnx. runs fine with cover off.

Do you have a remote, so you can read the error code? "Trips out" as a symptom description doesn't say much, but the self-diagnostic error codes can sometimes zoom right in.

Takagi's telephone tech-help would be the next step, but have the manual in front of you when you call.

Unit works fine with the cover off or bottom screws left off so the bottom hangs out letting it get more air. Tighten the screws, & it will trip the internal breaker & cover has to be removed to reset it, Don't get any codes. always worked fine till I had the cover off to replace the water control valve. any help greatly appreciated.

THE unit seems to have cleared itself up, Works fine now with the cover secured.