No hot water

Hi A few months ago my landlord had installed in my apartment a Laars Endurance boiler. Everything working fine until tonight. Went to take a shower and ran out of hot water. I went to look at the boiler and the message center said LO I turned off the emergency switch on the wall for a few minutes and turned it on again but all the boiler does is start up aand the message center reading is 118 then immediately displays 67 and then goes back to LO right away. Been trying to get my plumber for 2 hours. Anything I can do on my own to rectify this.
Thanks Barbara
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