Remove an Airlock from Your Hot Water System

Ever switched off and drained your hot water system to fix a leak, only to turn on your water and find no hot water?

Steps

Make sure your hot water supply is on.
If the cold water runs OK, but the hot water doesn't, or runs slowly then trickles off, then you may have an airlock, which is when air in the pipes isn't being moved by the hot water, thereby blocking the pipe.
Take a length of garden hose (about 1 foot) and some duct tape.
Use the duct tape and hose to connect the cold water tap to the hot water tap.
Open the hot water tap.
Open the cold water tap for 3-5 seconds.
Make sure that your airlock is fixed!
Check the hot water at another tap.
Repeat steps 5-8 two or three times.
IF the hot water is working, switch off all taps and remove your hose.
If not, call a plumber!!

Disconnect the blue pipe from the back of the washing machine.
Disconnect the red pipe that leads from the washing machine to the hot water pipe (i.e. the end that is not connected to the hot water connection of the washing machine
Connect the end of the blue pipe that was connected to the washing machine to where you just removed the red pipe
This now creates a 'U' between the cold and hot water pipes.
Open the hot water tap.
Open the cold water tap for 3-5 seconds.
Make sure that your airlock is fixed!
Check the hot water at another tap.
Repeat steps 5-8 two or three times.
IF the hot water is working, switch off all taps and remove your hose.
If not, call a plumber!!

Check that your airlock is fixed, after all this.
Similar techniques can be followed by using a mixer shower: Block the water from coming out of the shower head, with say a thin plastic bag placed over the pipe

Hot water can scald, even if there is an airlock.
Do NOT use either method if you have a pump pressurizing the system for power showers, etc.