No hot water pressure - perhaps sediment clogging exit pipe from water heater
It is fairly unlikely for boiler deposits/sediment to have blocked the outlet pipe as it is at the top of the tank, it is large, and sediment (by definition) settles to the bottom. I have never seen an "exit pipe filter screen".

A common problem is old shut-off valves not opening back up completely after they have been exercised. Another problem I have seen are these gimmick "heat-trapping" nipples installed at the heater inlet, they have little ball-check valves that fail and restrict water flow.

I live in an area with hard water (lots of minerals/dissolved solids) and I have never backflushed my water heater; it has been in service for 16 years with no problems. I am not saying you should not do it, I am just saying that the value is overrated when it comes to longevity (efficiency is another story).