I have no hot water heater in my house. The hot water comes directly off the boiler and expansion tank. Recently, the level of hot water available anywhere in the house has dropped to almost nothing (20 seconds of hot water, then cool water only). The baseboard heating system still works fine, only hot water at all faucets has been impacted. What could cause this/what can fix this? Thanks.
The answer is not so much what can fix this, but who can fix this. You need an experienced plumber to look at the way this system is piped to correct the problem. You can see how the devices are usually installed in the free hot water heating desing courses at: http://www.hydronic.net