I've been defeated by a hot water supply problem in my daughter's
house. The pressure is OK when you open the tap but then drops off
steadily to something just a bit more than a healthy trickle over about
a minute. She can get enough to do the washing up etc, but showering
is hopeless. The problem appeared suddenly about a week before
Christmas. Always a bit difficult to judge what 'suddenly' means from
the non-technical but her partner is reasonably switched on and he
agrees to that.

The house is 1950's terrace and is two storey with a traditional vented
dhw system heated by an indirect coil from a modern gas CH system. The
header tank is modern plastic with a cover and it's base is some 4 feet
off the attic floor - it looks clean inside. The hw tank is on the
floor of the bedroom below. The kitchen and bathroom are on the ground
floor next to one another and fed with a 3/4" pipe; the kitchen sink,
bathroom basin and shower all show the same characteristic.

I drained the header tank, removed the 22mm hw feed gate valve and
checked that for a blockage. I also took off a compression T feeding
the vent pipe (it was the only thing that was easily accessible and
helped to look as if I knew what I was doing !) and checked for
something coming down the vent pipe; everything was clean. There are
no isolator valves in the main hw supply pipe (that I could find
anyway!)

Anybody got any ideas other than something to do with the hw tank
itself; removing that is going to be a pig !! There's no drain point
to start with.

Any help would be appreciated - thanks

Rob

In an earlier contribution to this discussion,
wrote:

I've been defeated by a hot water supply problem in my daughter's
house. The pressure is OK when you open the tap but then drops off
steadily to something just a bit more than a healthy trickle over
about a minute. She can get enough to do the washing up etc, but
showering is hopeless. The problem appeared suddenly about a week
before Christmas. Always a bit difficult to judge what 'suddenly'
means from the non-technical but her partner is reasonably switched
on and he agrees to that.

The house is 1950's terrace and is two storey with a traditional
vented dhw system heated by an indirect coil from a modern gas CH
system. The header tank is modern plastic with a cover and it's base
is some 4 feet off the attic floor - it looks clean inside. The hw
tank is on the floor of the bedroom below. The kitchen and bathroom
are on the ground floor next to one another and fed with a 3/4" pipe;
the kitchen sink, bathroom basin and shower all show the same
characteristic.

I drained the header tank, removed the 22mm hw feed gate valve and
checked that for a blockage. I also took off a compression T feeding
the vent pipe (it was the only thing that was easily accessible and
helped to look as if I knew what I was doing !) and checked for
something coming down the vent pipe; everything was clean. There are
no isolator valves in the main hw supply pipe (that I could find
anyway!)

Anybody got any ideas other than something to do with the hw tank
itself; removing that is going to be a pig !! There's no drain point
to start with.

Any help would be appreciated - thanks

Rob

Sounds like either a blockage or an air-lock - although it's hard to explain
why it flows ok for the first minute or so.

Have you tried back-flushing it? Assuming that the cold tap is mains fed,
connect the hot and cold taps together with a short piece of hose and open
both taps - hot first fully, and then cold, gently. That will force water
backwards into the header tank - and is the usual cure for this type of
problem. You need an assistant to watch the header tank to ensure that it
doesn't overflow *and* to make sure that some water is flowing into it from
the bottom connection. [What you *mustn't* do is subject the hot cylinder to
full mains pressure - which might happen if there's a serious blockage
between the cylinder and header tank, and you turn on the cold tap too
fast].
--
Cheers,
Set Square
______
Please reply to newsgroup. Reply address is invalid.

wrote:
I've been defeated by a hot water supply problem in my daughter's
house. The pressure is OK when you open the tap but then drops off
steadily to something just a bit more than a healthy trickle over about
a minute. She can get enough to do the washing up etc, but showering
is hopeless. The problem appeared suddenly about a week before
Christmas. Always a bit difficult to judge what 'suddenly' means from
the non-technical but her partner is reasonably switched on and he
agrees to that.

The house is 1950's terrace and is two storey with a traditional vented
dhw system heated by an indirect coil from a modern gas CH system. The
header tank is modern plastic with a cover and it's base is some 4 feet
off the attic floor - it looks clean inside. The hw tank is on the
floor of the bedroom below. The kitchen and bathroom are on the ground
floor next to one another and fed with a 3/4" pipe; the kitchen sink,
bathroom basin and shower all show the same characteristic.

I drained the header tank, removed the 22mm hw feed gate valve and
checked that for a blockage. I also took off a compression T feeding
the vent pipe (it was the only thing that was easily accessible and
helped to look as if I knew what I was doing !) and checked for
something coming down the vent pipe; everything was clean. There are
no isolator valves in the main hw supply pipe (that I could find
anyway!)

Anybody got any ideas other than something to do with the hw tank
itself; removing that is going to be a pig !! There's no drain point
to start with.

Any help would be appreciated - thanks

Rob

1 minute is header tank time, not hw tank time. My best guess is your
header tank ballcock is only slowly dribble filling the header tank.
Once you've exhausted the header, the pressure head then falls from
header tank heoght to hw tank height, so you then only get low output.

If this is right, you'll find the ballcock only provides an inadequate
fill rate, and the header runs dry after a minute or so of tap full on.


NT

wrote:
robkgraham wrote:
I've been defeated by a hot water supply problem in my daughter's
house. The pressure is OK when you open the tap but then drops off
steadily to something just a bit more than a healthy trickle over about
a minute.

1 minute is header tank time, not hw tank time. My best guess is your
header tank ballcock is only slowly dribble filling the header tank.
Once you've exhausted the header, the pressure head then falls from
header tank heoght to hw tank height, so you then only get low output.

The cold water tank should hold much more water than this. To the
OP, what size is your header tank (resists any attempts at jokes)?

In article .com,
wrote:
I've been defeated by a hot water supply problem in my daughter's
house. The pressure is OK when you open the tap but then drops off
steadily to something just a bit more than a healthy trickle over about
a minute. She can get enough to do the washing up etc, but showering
is hopeless. The problem appeared suddenly about a week before
Christmas. Always a bit difficult to judge what 'suddenly' means from
the non-technical but her partner is reasonably switched on and he
agrees to that.

Airlock.

--
*This message has been ROT-13 encrypted twice for extra security *

Dave Plowman London SW
To e-mail, change noise into sound.

In article .com,
wrote:
I've been defeated by a hot water supply problem in my daughter's
house. The pressure is OK when you open the tap but then drops
off steadily to something just a bit more than a healthy trickle
over about a minute.

That sounds like a partial blockage, somewhere between
the outlet of the c/w tank and the outlet at the top
of the h/w tank, (before the vent pipe take-off).

The initial apparently healthy flow is the water
stored in the vent pipe. When that empties, the
draw is from the h/w tank, flow-rate limited by
the blockage.

Shut the tap off, and the vent pipe slowly refills,
ready for the next attempt.

Anybody got any ideas other than something to do with the hw tank
itself;..........

No words of comfort there.

Crud from the c/w tank settling at the base of
the feed pipe to the h/w tank?

Hard water area, chalk settling in the base of the
h/w tank? Try tapping down the side of the tank,
see if the sound changes as you reach the bottom.

.......... removing that is going to be a pig !!
There's no drain point to start with.

Who on earth plumbed in a h/w tank without allowing
a means to drain and replace it?

--
Tony Williams.

Header tank - big one ! (60 gallons at least I reckon) and there is no
way that it's level is going to drain down to cause this problem; it
took something like 20 minutes to drain it down through the bathroom
tap.

Assuming that the cold tap is mains fed,
connect the hot and cold taps together with a short piece of hose and
open
both taps - hot first fully, and then cold, gently.

I like Set Squares idea. I'll drain the c/w tank down first a bit I
think but that is the sort of tip I was looking for. Many thanks.

Who on earth plumbed in a h/w tank without allowing
a means to drain and replace it?

Actually there is a possible drain pipe that disappears down the back
to somewhere on the ground floor where there is now a gas fire with the
CH heater, but not knowing anything about these things I would need to
get a gas fitter in to get access to this pipe if indeed it does exist
- I suspect siphoning with a hose from the DHW tank top outlet would be
easier and less expensive.

Thanks guys

Rob