My house has a gas based water heater(geyser) on the outside. The plumber has connected it such that without the use of electric pump, just through pressure alone, hot water reaches the 1st and 2nd floor. How does this work?
Water – How does water flow through the water heater and up to the top floor without a pump
hot-waterwater-heaterwater-pressure
Related Solutions
I've been looking into a heat pump replacement.
You said "However, when the heat pump is in heating mode, the exiting refrigerant line is actually colder, not hotter, than when it enters. As a result, you cannot heat water during the winter."
That will depend on the location of the internal connections. The HP models I have seen with a desuperheater ( hot water generator ) place the HWG after the compressor before the reversing valve. That means the pump always runs forward, the HWG always has hot refrigerant to use and it works in summer and in winter. The reversing valve does just that - in summer it sends the leftover heat to the outside and extracts heat (cools) the inside. In winter it sends the heat to the inside and extracts heat from the outside. 
First thing to check is the faucet aerator. You're probably right about kicking sediment up and clogging something, if you're lucky its just the aerator. It'd take a big piece or a lot of sediment to completely clog a 1/2"-3/4" pipe.
If it's not the aerator, and it's just a single faucet, you have to work backwards starting with the supply lines connecting the faucet to the shut-off valve, all the way back to the water heater.
Related Topic
- Water – How to prevent pressure from dropping from the water heater
- Water – How to measure water pump pressure in a spa heating system
- Plumbing – Flow sensor adjustment for Navien 240S natural gas fired tankless water heater
- Water – Hot water flow is slow from 3 L/3KW instant geyser (hot water heater)
- Water – How does a gas water heater thermostat and gas valve work
- Plumbing – Can a tankless water heater outlet pressure be increased without a second heater
- Water – Why does the water heater’s drain line rejoin the outlet pipe
- Water Heater – Electric Heat Pump with Solar vs. Gas Water Heater
Best Answer
The same pressure (provided by your local utility)that pushes the water out of the first floor faucet. It all requires pressure. The water heater provides very little resistance to the flow of the water.