Loss of hot water pressure

[kipper]

I have a gravity fed hot water system. Until recently it had a health

system presssure. No changes have been made to the system and no recen work has been carried out. Pressure has dropped off to the point wher it can take 20 minutes to run a bath. There has been a correspondin drop (although not quite as significant) in cold water presure Pressure starts good and tails off as if a down pipe were emptying bu not being backed up.

All valves feeding the header tanks seem to be open and depressing th ballcocks results in appropriate water flow into the tanks

-- kipper

[Christian McArdle]

Probably either exceptionally bad scaling up of pipework, or a broken (or mostly closed) gate valve between the cold tank and the bottom of the hot water cylinder.

Christian.

[Set Square]

You've got either a blockage or an air-lock in the pipes. Does this happen with all hot taps, or only on the bath? Does the cold water for the bath also come from the header tank, or direct from the mains?

The standard cure is to backflush the pipework with mains pressure. If the bath cold supply is mains, you need to connect hot and cold taps together, and turn them both on - hot first. This will get rid of any air lock and push any blockage back into the header tank. Only turn on the cold tap gently until you're sure that water is flowing back into the header. If there's a solid blockage, you could get full mains pressure in the hot water cylinder with undesirable consequences!

If the bath tap cold supply comes from the header, you'll need to find a mains cold supply somewhere else (kitchen tap?) and use a hosepipe to connect it to the bath tap. In this case, you'll need to back-flush both hot and cold bath taps.

[Aidan]

I had this with a tank where bits of loft insulation had got into the water. The insulation got stuck upstream of the service valves (non-full bore ball valves) and restricted the water flow.

[Aidan]

PS Some taps have screw-on mesh strainers on the outlets. I think they're supposed to aereate the water or summat. They can get clogged with limescale, restricting flow. Unscrew, descale, refit.

[Doctor Evil]

Aiden wrote to himself.

Aerators on taps reduce water consumption. In Germany most taps are of this sort and many have flow reducers in the aerator tip. It is regarded as the housewives task to maintain these. She unscrews, cleans, or replaces from the supermarket. No plumber involved.

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[kipper]

Things have got worse. Down to a trickle now.

The outlet stop tap on the exit from the header tank seemed not b engaging. So I got it into my head it was blocked. I did a quick an dirty temporary "repair" by cutting out the tap and putting in straigh pipe. The tap did seem blocked but its removal hasn't cleared th problem.

Answers gratefully received

-- kipper

[Aidan]

Dr. Evil wrote

snip Drivel/Dr. Evil

Something of no relevance about hausfraus and information recycled from earlier posters, who had managed to be useful and inoffensive.

[John]

Has a dead bird found its way into the outlet from the header tank?

[Doctor Evil]

< snip drivel>

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[Aidan]

Try back-flushing it.

Drain the tank; tie up the ball-float and run some water out. If you've got a kitchen mixer tap, you can sometimes flush it by holding a food bag over the spout & turning on the hot and then the cold mains (slowly). The high pressure cold water will go up the hot pipe.

Otherwise, you can disconnect the washing machine hoses and connect one hose between the hot and cold taps. The cold is usually mains. Having someone watch the tank to see what comes out is an advantage.

[Aidan]

Are all the taps affected or just the bath taps?

[kipper]

Loss occurred gradually with reduced pressure for a week or two followe

by complete loss of pressure Friday evening.

When any hot tap is opened there is an initial flow of water which the dries up. If the tap is closed for several minutes and reopened there i another initial flow implying some slow flow of water into the system.

The header tank is full and the exit from the tank is clear.

We the disconnected the inflowing pipe to the stop tap immediatel before the hot water tank there was a strong flow of water and goo pressure at this point.

We have tried driving mains cold water through the system. The pipes t the taps fill but there is no flow up the water outlet of the heade tank. Instead flow comes through the boiler vent pipe back into th header tank.

It has been suggested to us that the valve at the top of the hot wate tank is one which prevents back flow and so we are not driving an water into the hot water tank to clear the air-block.

Is it worth trying to drain down the whole system? If so, how do you g about this

-- kipper

[Set Square]

I presume you mean the vent pipe which comes off the top of the hot cylinder - which provides an easier path for the water than going backwards through the cylinder and up the feed pipe.

In that case, you'll need to block the vent pipe temporarily while you back-flush.