Oil heater hot water problem

I have an oil heater with baseboard heat and it heats the hot water. Since yesterday morning the water in the showers comes out hot for about 25 seconds and then turns cold. Same with all the sinks, washers and dishwashers. The house is warm and the heater is running okay, no odd noises. The only thing different was I turned up the heat upstairs from 65 to 70 because it was chilly up there.
Is there anything easy I can check? Could something have switched off?
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Scout Lady wrote:

You have a hot water boiler with a domestic water coil in it right? Check that the water temperature in the boiler is hot (probably 180 F). If thats ok then if you have a bypass valve that regulates the hot water temperature by feeding some cold into the outgoing hot line if its too hot, check that that is working correctly. Another possibility (slim chance and probably not the problem) is the domestic coil is bad, you would need to shut down and cool down the boiler, lock it out, drain the boiler water, and visually inspect the outside of the domestic coil if possible. See if its coated with crud, or if it has fins, did they rot off etc etc, you'd be looking for something that impedes heat transfer. If you do this step, be sure and refill boiler with proper water , bleed of trapped air, and add whatever chemicals are required (ie rust inhibitors, antifreeze or whatever is required) (see your owners manual) Eric
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