Customer is losing hot water after a few seconds of running faucet. Temperature began at 140 coming from faucet and dropped to 95. Tried adjusting low limit and differential but I was still losing the hot water. Spoke with Kurt and we began trying different attempts to get the hot water back. We shut off cold side valve completely which gave hot water immediately for a long period of time, however when I slightly opened valve back up the faucet temperature immediately began to drop back into 90s. Water coil and boiler are both from 1990. Coil needs to be flushed however with boiler being so old I do not recommend as bolts are very old and runs the possibility of breaking when trying to remove coil for repair. Highly recommend replacing boiler due to age. Gave customer options for calcium flush, electric water heater, informer customer price for electric water heater would be different due to electricians needing to come out and run wire to panel. There is access and open spots on panel