My water pressure is down to a trickle for hot water upstairs. Seems to be oK for cold water and for water on the main floor. What's the problem? Thanks

So you are saying hot is a trickle every where in the house, right? Makes me thin we have an issue with the heater. Tell me about your water heater and have you opened the boiler drtain valve on the bottom recently?

No the trickle is only on the hot water faucets in the upstairs bath. The rest of the house is fine.

How many faucets up stairs suffering this problem? What kind of faucets, tub, lavatory? Same bath or different baths.

Yep, we need to know if its just one faucet or muiltiple faucets and/or tub.