Sorry but this is a bit of a long story.

Earlier in the year we had a problem with intermittent discharge from
an unvented hot water cylinder (the installation was around 4 years
old).

The book says this could be caused by low pressure in the expansion
vessel, so I checked it by shutting off the cold water feed to the
cylinder, reducing the pressure in the cylinder by operating a hot tap,
and putting a tyre valve on the expansion vessel. The pressure was
extremely low so I repressurised it using a car foot pump.

This didn't solve the problem.

The book says the other reason could be back pressure (crossflow).

Another symptom we experienced was that when you operated a hot tap,
instead of the water running warm or hot from previous use as you would
expect, it would actually run warm very briefly, then go icy cold, and
then eventually hot again.

It seemed clear that cold water was being admitted into the hot water
circuit somewhere.

Then the shower started to go wrong: it gradually got colder and we had
to keep turning the thermostat up and eventually it would only run
cold.

The shower is of an interesting design, which is that the hot and cold
feeds go to the thermostatic cartridge first, which then feeds the flow
valve, rather than having flow valves on the hot and cold feeds.

It seemed obvious that the thermostatic cartridge was failing and
allowing cold water back into the hot water system. In any case, it
seemed impossible for the problem to be caused by anything else (the
only other places the hot water goes to are four mixer taps and the
washing machine). The problem occurred without any of these taps being
operated. Some of these other taps have isolating valves and when I
shut them off the problem was still there. So, surely, it was the
shower.

We had the shower replaced and the problem seemed to go away but
quickly came back. Could the shower have failed again so quickly?
Anyway, we got a replacement, but the problem was still there. So we
got another replacement, fitted today, and the problem is *still*
there.

Now, you might say, the thing is surely to operate the isolating valves
to the shower and prove that beyond any doubt that it is the fourth
faulty shower in a row. However, there are no isolating valves, and to
fit any, and make them accessible, would mean ripping the bathroom
apart and taking out the bath, and running long pipe loops to somewhere
accessible and putting isolating valves in the loops - costing a small
fortune and creating huge disruption. (Alternatively, I suppose, we
could fairly easily gain access to the pipes from outside, by ripping
off the external cladding - timber framed / walled house.)

In any case, I really don't see how it could be anything else apart
from the shower. Mixer taps don't tend to admit cold water to the hot
water circuit, especially when they're not being operated.

Any ideas anyone please?

Andrew

"Winelight" wrote in message
oups.com...
Sorry but this is a bit of a long story.

Earlier in the year we had a problem with intermittent discharge from
an unvented hot water cylinder (the installation was around 4 years
old).

The book says this could be caused by low pressure in the expansion
vessel, so I checked it by shutting off the cold water feed to the
cylinder, reducing the pressure in the cylinder by operating a hot tap,
and putting a tyre valve on the expansion vessel. The pressure was
extremely low so I repressurised it using a car foot pump.

This didn't solve the problem.

The book says the other reason could be back pressure (crossflow).

Another symptom we experienced was that when you operated a hot tap,
instead of the water running warm or hot from previous use as you would
expect, it would actually run warm very briefly, then go icy cold, and
then eventually hot again.

It seemed clear that cold water was being admitted into the hot water
circuit somewhere.

Then the shower started to go wrong: it gradually got colder and we had
to keep turning the thermostat up and eventually it would only run
cold.

The shower is of an interesting design, which is that the hot and cold
feeds go to the thermostatic cartridge first, which then feeds the flow
valve, rather than having flow valves on the hot and cold feeds.

It seemed obvious that the thermostatic cartridge was failing and
allowing cold water back into the hot water system. In any case, it
seemed impossible for the problem to be caused by anything else (the
only other places the hot water goes to are four mixer taps and the
washing machine). The problem occurred without any of these taps being
operated. Some of these other taps have isolating valves and when I
shut them off the problem was still there. So, surely, it was the
shower.

We had the shower replaced and the problem seemed to go away but
quickly came back. Could the shower have failed again so quickly?
Anyway, we got a replacement, but the problem was still there. So we
got another replacement, fitted today, and the problem is *still*
there.

Now, you might say, the thing is surely to operate the isolating valves
to the shower and prove that beyond any doubt that it is the fourth
faulty shower in a row. However, there are no isolating valves, and to
fit any, and make them accessible, would mean ripping the bathroom
apart and taking out the bath, and running long pipe loops to somewhere
accessible and putting isolating valves in the loops - costing a small
fortune and creating huge disruption. (Alternatively, I suppose, we
could fairly easily gain access to the pipes from outside, by ripping
off the external cladding - timber framed / walled house.)

In any case, I really don't see how it could be anything else apart
from the shower. Mixer taps don't tend to admit cold water to the hot
water circuit, especially when they're not being operated.

Any ideas anyone please?

Andrew

Are the other tap mixers in the house OK? You can take off the shower mixer
and connect up a hose and temporary tap and see if hot comes out of the hot
pipe.

Unvented cylinders are famous for back flow from cold supplies Also you
could fit a non-return valve in the hot supply of all the mixer taps in the
house. Then any water passing crossing over through the mixer will be
checked A compression non-return valve will fit easily onto the pipes. Or
if the shower mixer pipe goes back to the cylinder (which it should), then
maybe one non-return on the hot draw-off pipe to all the outlets except the
shower would do it.

First see if hot water is actually at the shower mixer valve. You may have
a blockage. Then install the non-return valves at the mixers as a matter of
course. http://www.bes.co.uk sell them cheap enough.

On Nov 15, 2:43 am, "Winelight" wrote:
Sorry but this is a bit of a long story.
Any ideas anyone please?

Andrew

Backflow?

There's a connection on the multi-function/combination valve (check
valve + pressure reducing valve + pressure relief valve) for the cold
supply. This is so the cold is at the same pressure as the hot. It's
often not used where, for example the system is converted from a
storage tank supply or is connected to the mains at ground floor level
& it's too inconvenient for the plumber to do the job properly. Read
the manual.

If the cold is connected direct to the mains and doesn't pass through
the combination valve, there can be problems. Connect it to the fitting
provided or, failing that, install a pressure reducing valve on it.

Aidan wrote:

If the cold is connected direct to the mains and doesn't pass through
the combination valve, there can be problems.

Yes, that's how it is. The original installer failed to take a separate
cold feed from the pressure-reduced output but instead connected
everything to the mains.

Connect it to the fitting
provided or, failing that, install a pressure reducing valve on it.

Thanks for the suggestions. The latter option is also what the plumber
reckoned was the best bet.

However before embarking on that I wanted to be 100% certain that the
shower is the cause of the problem. It just seemed odd that one shower
worked for 4 years, and then three more exhibited a fault that the
first one didn't, if you see what I mean.

Andrew

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

If the cold is connected direct to the mains and doesn't pass through
the combination valve, there can be problems.

Yes, that's how it is. The original installer failed to take a separate
cold feed from the pressure-reduced output but instead connected
everything to the mains.

Connect it to the fitting
provided or, failing that, install a pressure reducing valve on it.

Thanks for the suggestions. The latter option is also what the plumber
reckoned was the best bet.

However before embarking on that I wanted to be 100% certain that the
shower is the cause of the problem. It just seemed odd that one shower
worked for 4 years, and then three more exhibited a fault that the
first one didn't, if you see what I mean.

Andrew

Getting two pressure reducing valves to operate at the same pressure
constantly is difficult. If you do fit one on the cold mains supply, then
find out what the pressure is at the DHW draw-off at the top of the cylinder
and set it to that. There is a pressure loss across the cylinder. Even
taking the cold off the combination valve still leads to an imbalance
between hot and cold, athough not great, as there is a pressure loss across
the cylinder.

This is another point where heat banks (using plate heat exchanger) score
over unvented cylinders. If the plate is say, rated at 10 bar and so is the
shower mixer, then there is no need for a pressure reducing valve if the
pressure is even 6 bar. A shower mixer with a pressure equalisation valve
can trim off any slight imbalance. Also the lack of a cylinder means no
crossover problems.

If it is difficult to get a cold supply pipe back to the combination valve,
I would be tempted to use non-return valves. They are cheaper and less
likely to go wrong.

Fist find out if there is hot water at the hot pipe at the shower.

Doctor Drivel wrote:

This is another point where heat banks (using plate heat exchanger) score
over unvented cylinders. If the plate is say, rated at 10 bar and so is the

Well, yes, it's tempting to replace the whole thing with a thermal
store. Expensive, yes, but at the right I'm running up plumber's bills
to keep changing the shower...!

I would be tempted to use non-return valves. They are cheaper and less
likely to go wrong.

OK, thanks. I'll read what you said again more carefully to make sure I
understand where they have to go.

Fist find out if there is hot water at the hot pipe at the shower.

Sorry, I should have been more precise. The current shower, fitted
yesterday, does actually work, it's just that we are clearly getting
mains cold water back into the hot water system through the outlet
pipe. (The first shower, when it failed, did also behave like this for
a while before the thermostatic cartridge failed altogether resulting
in cold showers only.) So yes, there must be hot water getting to the
shower.

Andrew

On Nov 15, 7:01 pm, "Winelight" wrote:
Doctor Drivel wrote:

I would be tempted to use non-return valves. They are cheaper and less
likely to go wrong.

Less likely to work, too

They'll stop the cold water flowing backwards up the hot pipes.
However, the hot water at, let's say, 3 bar won't be able to flow into
the shower valve if the shower valve is full of cold water at 6 bar.

Best to ignore Drivel, except for the purposes of entertainment. He's
well known for his rantings.

You can buy shower valves that work with supplies at unbalanced
pressures, usually mains cold and hot from a tank via a cylinder.

"Winelight" wrote in message
ups.com...
Doctor Drivel wrote:

This is another point where heat banks (using plate heat exchanger) score
over unvented cylinders. If the plate is say, rated at 10 bar and so is
the

Well, yes, it's tempting to replace the whole thing with a thermal
store. Expensive, yes, but at the right I'm running up plumber's bills
to keep changing the shower...!

It is easy to convert as a DIY task to a heat bank.

I would be tempted to use non-return valves. They are cheaper and less
likely to go wrong.

OK, thanks. I'll read what you said again more carefully to make sure I
understand where they have to go.

Fist find out if there is hot water at the hot pipe at the shower.

Sorry, I should have been more precise. The current shower, fitted
yesterday, does actually work, it's just that we are clearly getting
mains cold water back into the hot water system through the outlet
pipe. (The first shower, when it failed, did also behave like this for
a while before the thermostatic cartridge failed altogether resulting
in cold showers only.) So yes, there must be hot water getting to the
shower.

Andrew

"Winelight" wrote in message
oups.com...
Sorry but this is a bit of a long story.

Earlier in the year we had a problem with intermittent discharge from
an unvented hot water cylinder (the installation was around 4 years
old).

The book says this could be caused by low pressure in the expansion
vessel, so I checked it by shutting off the cold water feed to the
cylinder, reducing the pressure in the cylinder by operating a hot tap,
and putting a tyre valve on the expansion vessel. The pressure was
extremely low so I repressurised it using a car foot pump.

This didn't solve the problem.

The book says the other reason could be back pressure (crossflow).

Another symptom we experienced was that when you operated a hot tap,
instead of the water running warm or hot from previous use as you would
expect, it would actually run warm very briefly, then go icy cold, and
then eventually hot again.

It seemed clear that cold water was being admitted into the hot water
circuit somewhere.

Then the shower started to go wrong: it gradually got colder and we had
to keep turning the thermostat up and eventually it would only run
cold.

The shower is of an interesting design, which is that the hot and cold
feeds go to the thermostatic cartridge first, which then feeds the flow
valve, rather than having flow valves on the hot and cold feeds.

It seemed obvious that the thermostatic cartridge was failing and
allowing cold water back into the hot water system. In any case, it
seemed impossible for the problem to be caused by anything else (the
only other places the hot water goes to are four mixer taps and the
washing machine). The problem occurred without any of these taps being
operated. Some of these other taps have isolating valves and when I
shut them off the problem was still there. So, surely, it was the
shower.

We had the shower replaced and the problem seemed to go away but
quickly came back. Could the shower have failed again so quickly?
Anyway, we got a replacement, but the problem was still there. So we
got another replacement, fitted today, and the problem is *still*
there.

Now, you might say, the thing is surely to operate the isolating valves
to the shower and prove that beyond any doubt that it is the fourth
faulty shower in a row. However, there are no isolating valves, and to
fit any, and make them accessible, would mean ripping the bathroom
apart and taking out the bath, and running long pipe loops to somewhere
accessible and putting isolating valves in the loops - costing a small
fortune and creating huge disruption. (Alternatively, I suppose, we
could fairly easily gain access to the pipes from outside, by ripping
off the external cladding - timber framed / walled house.)

In any case, I really don't see how it could be anything else apart
from the shower. Mixer taps don't tend to admit cold water to the hot
water circuit, especially when they're not being operated.

Any ideas anyone please?

Andrew

Another point. Has the water pressure gone up from the street after some
works on the mains? If say they have upped it to 6 bar and shower mixer
valve is rated for 4 bar maximum then it may be early failure for the valve.

Doctor Drivel wrote:

"Winelight" wrote in message
oups.com...
Sorry but this is a bit of a long story.

Earlier in the year we had a problem with intermittent discharge from
an unvented hot water cylinder (the installation was around 4 years
old).

The book says this could be caused by low pressure in the expansion
vessel, so I checked it by shutting off the cold water feed to the
cylinder, reducing the pressure in the cylinder by operating a hot tap,
and putting a tyre valve on the expansion vessel. The pressure was
extremely low so I repressurised it using a car foot pump.

This didn't solve the problem.

The book says the other reason could be back pressure (crossflow).

Another symptom we experienced was that when you operated a hot tap,
instead of the water running warm or hot from previous use as you would
expect, it would actually run warm very briefly, then go icy cold, and
then eventually hot again.

It seemed clear that cold water was being admitted into the hot water
circuit somewhere.

Then the shower started to go wrong: it gradually got colder and we had
to keep turning the thermostat up and eventually it would only run
cold.

The shower is of an interesting design, which is that the hot and cold
feeds go to the thermostatic cartridge first, which then feeds the flow
valve, rather than having flow valves on the hot and cold feeds.

It seemed obvious that the thermostatic cartridge was failing and
allowing cold water back into the hot water system. In any case, it
seemed impossible for the problem to be caused by anything else (the
only other places the hot water goes to are four mixer taps and the
washing machine). The problem occurred without any of these taps being
operated. Some of these other taps have isolating valves and when I
shut them off the problem was still there. So, surely, it was the
shower.

We had the shower replaced and the problem seemed to go away but
quickly came back. Could the shower have failed again so quickly?
Anyway, we got a replacement, but the problem was still there. So we
got another replacement, fitted today, and the problem is *still*
there.

Now, you might say, the thing is surely to operate the isolating valves
to the shower and prove that beyond any doubt that it is the fourth
faulty shower in a row. However, there are no isolating valves, and to
fit any, and make them accessible, would mean ripping the bathroom
apart and taking out the bath, and running long pipe loops to somewhere
accessible and putting isolating valves in the loops - costing a small
fortune and creating huge disruption. (Alternatively, I suppose, we
could fairly easily gain access to the pipes from outside, by ripping
off the external cladding - timber framed / walled house.)

In any case, I really don't see how it could be anything else apart
from the shower. Mixer taps don't tend to admit cold water to the hot
water circuit, especially when they're not being operated.

Any ideas anyone please?

Andrew

Another point. Has the water pressure gone up from the street after some
works on the mains? If say they have upped it to 6 bar and shower mixer
valve is rated for 4 bar maximum then it may be early failure for the valve.

Not as far as I know (or have noticed). The shower mixer valve is rated
at 3 bar. Whether or not the mains is greater than that I do not know.
Even so it seems unlikely that two or three showers in a row would fail
instantanously in this way, I'd have thought?

Andrew

"Winelight" wrote in message
oups.com...
Doctor Drivel wrote:

"Winelight" wrote in message
oups.com...
Sorry but this is a bit of a long story.

Earlier in the year we had a problem with intermittent discharge from
an unvented hot water cylinder (the installation was around 4 years
old).

The book says this could be caused by low pressure in the expansion
vessel, so I checked it by shutting off the cold water feed to the
cylinder, reducing the pressure in the cylinder by operating a hot tap,
and putting a tyre valve on the expansion vessel. The pressure was
extremely low so I repressurised it using a car foot pump.

This didn't solve the problem.

The book says the other reason could be back pressure (crossflow).

Another symptom we experienced was that when you operated a hot tap,
instead of the water running warm or hot from previous use as you would
expect, it would actually run warm very briefly, then go icy cold, and
then eventually hot again.

It seemed clear that cold water was being admitted into the hot water
circuit somewhere.

Then the shower started to go wrong: it gradually got colder and we had
to keep turning the thermostat up and eventually it would only run
cold.

The shower is of an interesting design, which is that the hot and cold
feeds go to the thermostatic cartridge first, which then feeds the flow
valve, rather than having flow valves on the hot and cold feeds.

It seemed obvious that the thermostatic cartridge was failing and
allowing cold water back into the hot water system. In any case, it
seemed impossible for the problem to be caused by anything else (the
only other places the hot water goes to are four mixer taps and the
washing machine). The problem occurred without any of these taps being
operated. Some of these other taps have isolating valves and when I
shut them off the problem was still there. So, surely, it was the
shower.

We had the shower replaced and the problem seemed to go away but
quickly came back. Could the shower have failed again so quickly?
Anyway, we got a replacement, but the problem was still there. So we
got another replacement, fitted today, and the problem is *still*
there.

Now, you might say, the thing is surely to operate the isolating valves
to the shower and prove that beyond any doubt that it is the fourth
faulty shower in a row. However, there are no isolating valves, and to
fit any, and make them accessible, would mean ripping the bathroom
apart and taking out the bath, and running long pipe loops to somewhere
accessible and putting isolating valves in the loops - costing a small
fortune and creating huge disruption. (Alternatively, I suppose, we
could fairly easily gain access to the pipes from outside, by ripping
off the external cladding - timber framed / walled house.)

In any case, I really don't see how it could be anything else apart
from the shower. Mixer taps don't tend to admit cold water to the hot
water circuit, especially when they're not being operated.

Any ideas anyone please?

Andrew

Another point. Has the water pressure gone up from the street after some
works on the mains? If say they have upped it to 6 bar and shower mixer
valve is rated for 4 bar maximum then it may be early failure for the
valve.

Not as far as I know (or have noticed). The shower mixer valve is rated
at 3 bar. Whether or not the mains is greater than that I do not know.
Even so it seems unlikely that two or three showers in a row would fail
instantanously in this way, I'd have thought?

Screwfix sell a pressure gauge that you can connect to the washing machine
raps or outside hose connection. I would buy one and see what the pressure
is?

Good idea. I need to put in a Screwfix order anyway.

Andrew

Doctor Drivel wrote:

"Winelight" wrote in message
oups.com...
Doctor Drivel wrote:

"Winelight" wrote in message
oups.com...
Sorry but this is a bit of a long story.

Earlier in the year we had a problem with intermittent discharge from
an unvented hot water cylinder (the installation was around 4 years
old).

The book says this could be caused by low pressure in the expansion
vessel, so I checked it by shutting off the cold water feed to the
cylinder, reducing the pressure in the cylinder by operating a hot tap,
and putting a tyre valve on the expansion vessel. The pressure was
extremely low so I repressurised it using a car foot pump.

This didn't solve the problem.

The book says the other reason could be back pressure (crossflow).

Another symptom we experienced was that when you operated a hot tap,
instead of the water running warm or hot from previous use as you would
expect, it would actually run warm very briefly, then go icy cold, and
then eventually hot again.

It seemed clear that cold water was being admitted into the hot water
circuit somewhere.

Then the shower started to go wrong: it gradually got colder and we had
to keep turning the thermostat up and eventually it would only run
cold.

The shower is of an interesting design, which is that the hot and cold
feeds go to the thermostatic cartridge first, which then feeds the flow
valve, rather than having flow valves on the hot and cold feeds.

It seemed obvious that the thermostatic cartridge was failing and
allowing cold water back into the hot water system. In any case, it
seemed impossible for the problem to be caused by anything else (the
only other places the hot water goes to are four mixer taps and the
washing machine). The problem occurred without any of these taps being
operated. Some of these other taps have isolating valves and when I
shut them off the problem was still there. So, surely, it was the
shower.

We had the shower replaced and the problem seemed to go away but
quickly came back. Could the shower have failed again so quickly?
Anyway, we got a replacement, but the problem was still there. So we
got another replacement, fitted today, and the problem is *still*
there.

Now, you might say, the thing is surely to operate the isolating valves
to the shower and prove that beyond any doubt that it is the fourth
faulty shower in a row. However, there are no isolating valves, and to
fit any, and make them accessible, would mean ripping the bathroom
apart and taking out the bath, and running long pipe loops to somewhere
accessible and putting isolating valves in the loops - costing a small
fortune and creating huge disruption. (Alternatively, I suppose, we
could fairly easily gain access to the pipes from outside, by ripping
off the external cladding - timber framed / walled house.)

In any case, I really don't see how it could be anything else apart
from the shower. Mixer taps don't tend to admit cold water to the hot
water circuit, especially when they're not being operated.

Any ideas anyone please?

Andrew

Another point. Has the water pressure gone up from the street after some
works on the mains? If say they have upped it to 6 bar and shower mixer
valve is rated for 4 bar maximum then it may be early failure for the
valve.

Not as far as I know (or have noticed). The shower mixer valve is rated
at 3 bar. Whether or not the mains is greater than that I do not know.
Even so it seems unlikely that two or three showers in a row would fail
instantanously in this way, I'd have thought?

Screwfix sell a pressure gauge that you can connect to the washing machine
raps or outside hose connection. I would buy one and see what the pressure
is?