Water comes out of hot taps for about 4 seconds then nothing, this is with every hot tap. Everything was working fine previous to this.

Don't know if a piece of debris is clogging a passage, at water heater?

Everything the eye can see looks clear, checked the water cisterns in the attic. I suspect it is airlocked but trying to push cold water mains pressure back up the hot water pipe to clear the airlock hasn't worked yet...

I believe the Problem is at the Water Heater, or between the water heater and where all the hots split up through the house.
Everything you see WILL look clear, the problem is where you can't see in the pipes?

Need some more details, after 4 seconds do you still have water flow or there is no flow, how is your shower, does it works?

Thanks,
John

Ok, so in the kitchen I have a single tap with hot and cold lever, when turned to hot I get good flow for a few seconds but then it drains off to little, same in downstairs shower, tiny trickle, the bath is spluttering with really nothing coming. I was talking to someone who is in the business and he said it could be lime built up over the hot water cylinder on the bend of the pipe, but I have very little lime present in the kettle and the neighbor has never had problems with lime... just to be aware the taps do give good flow when they are turned on first, but then the flow reduces significantly to very little, thanks

Without a Plumber, I would turn off the Breaker to the Water Heater, attach a hose to the bottom and let it drain, maybe into something to see what the problem was.
Close up, refill, Breaker back on.
Its free and takes little time.

I would turn off the Breaker to the Water Heater, attach a hose to the bottom and let it drain, This is NOT how to flush out a heater. Here's how.
For long life and fewer troubles you should keep your heater clear of mineral build-up by FLUSHING NOT DRAINING on a regular schedule. Attach a hose to the boiler drain at the bottom of the tank. With the pressure on, open the boiler drain and let it run until the water runs clear. You will see a spurt of red,(rust) followed by white or yellow grains,(lime or calcium carbonate). This shouldn't take more then a few minutes. Do this monthly to keep it clear. Now flush out yourhot water lines on ALL fixtures that are affected . Now pull each aerator and clean the screens. Be sure you put them back together the same way you took them out. Don't forget to flush it out every month. Your heater will thank you for it.

checked the water cisterns in the attic. Are you located in the UK? Tell me more about this "cistern". Would this be the same thing as your "water cylinder"?
If not please explain.
How old is the hot water system?
Since all your hot water taps are affected I would start at the hot water heater.
Do you flush it our on a regular schedule? Would there be heat trap nipples (see image) installed on the inlet and output of the heater? Is the water heater gas nor electric? Back to you, Tom

Speedball, do those block or reduce flow if too hot?

Speedball, do those block or reduce flow if too hot?

No! A heat trap( see another type) contains the heat to the heater so it doesn't convect outside the heater. Regards, Tom

Interesting.

In response to flushing the system, I don't think this is something I would be comfortable doing, the hot water cylinder is upstairs so due to the risk of flooding I would not like to try this, if I do have to get a plumber I will suggest this though so thanks.
I am comfortable with turning off the mains water supply outside and draining the whole system if that helps.
When I say cistern I do not mean not cylinder, the hot water cylinder is my bath/sink hot water cylinder containing the elements to heat the water. Tom I do not flush regulary, I bought house in January, house is 3 years old, tank is electrically heated...
I am in Ireland. I have two water tanks (cisterns) in the attic, one to feed the upstairs tanks/toliets and the other is the overflow cistern.