I turn on the hot water faucet and cold water comes out. This happens everywhere around the house. Once I flush the single toilet that's on the first floor and wait 1-2 mins, hot water starts pouring out of the faucet. The second floor also has this issue where I have to flush the toilet on the second floor to get hot water anywhere on that floor. The hot water would continue to stay for about 1-3 days before having to repeat the flushing process again.
Read online that many place the blame on the water heater (which doesn't seem likely but would like to hear what you think) or the house having an old plumbing structure. If so, what can I do to fix it? Thanks!