Loss of hot water pressure
 

I have a gravity fed hot water system. Until recently it had a healthy system presssure. No changes have been made to the system and no recent work has been carried out. Pressure has dropped off to the point where it can take 20 minutes to run a bath. There has been a corresponding drop (although not quite as significant) in cold water presure. Pressure starts good and tails off as if a down pipe were emptying but not being backed up.

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

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

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.

In an earlier contribution to this discussion,
kipper wrote:

I have a gravity fed hot water system. Until recently it had a healthy
system presssure. No changes have been made to the system and no
recent work has been carried out. Pressure has dropped off to the
point where it can take 20 minutes to run a bath. There has been a
corresponding drop (although not quite as significant) in cold water
presure. Pressure starts good and tails off as if a down pipe were
emptying but not being backed up.

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

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.
--
Cheers,
Set Square
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Set Square wrote:
In an earlier contribution to this discussion,
kipper wrote:

Does your cold water storage tank have a tight-fitting lid?

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 wrote:

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.

"Aidan" wrote in message
oups.com...

Aidan wrote:

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.

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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Things have got worse. Down to a trickle now.

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

Answers gratefully received.

Dr. Evil wrote
Aerators on taps.....

snip Drivel/Dr. Evil

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

"kipper" wrote in message
...

I have a gravity fed hot water system. Until recently it had a healthy
system presssure. No changes have been made to the system and no recent
work has been carried out. Pressure has dropped off to the point where
it can take 20 minutes to run a bath. There has been a corresponding
drop (although not quite as significant) in cold water presure.
Pressure starts good and tails off as if a down pipe were emptying but
not being backed up.

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

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

"Aidan" wrote in message
ups.com...

snip drivel


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kipper wrote:
Things have got worse. Down to a trickle now.

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.

Are all the taps affected or just the bath taps?

Loss occurred gradually with reduced pressure for a week or two followed by complete loss of pressure Friday evening.

When any hot tap is opened there is an initial flow of water which then dries up. If the tap is closed for several minutes and reopened there is 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 immediately before the hot water tank there was a strong flow of water and good pressure at this point.

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

It has been suggested to us that the valve at the top of the hot water tank is one which prevents back flow and so we are not driving any 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 go about this?

In an earlier contribution to this discussion,
kipper wrote:


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

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.
--
Cheers,
Set Square
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