Hi All
I've just moved into a house that has hot water supplied by an electric
immersion heater. The small cold water tank is the top part of the hot
water cylinder. When running a bath the cold tank seems to empty far
quicker than it can refill from the mains. Consequently the hot water
starts to splurge out; still hot though.
Taking a shower which is fed from these tanks has woefully low pressure
and a piddly experience. I could put a pump on this but a shower would
then be short but sweet! And I could replace the cylinder with a loft
cold tank and standard hot water cylinder. There is also an electric
shower (10kW), but this too is rather poor.
So, I was considering a gas powered water heater to provide "continuous"
hot water at mains pressure. Several models seem to be available at the
£450 price point that have flow rates from 10 to 16 l/min. The central
heating is by warm air. Don't know how efficient these systems are.
My questions are (sorry, there are lots):
Do you need special gas pipework (wider) for these gas water heaters? I
couldn't find any reference to this in the installation instructions (or
didn't know what to look for). I will not be fitting it myself.
Are the following brands any good: Ariston, Rinnai, Main, Vokera. Any
others that may be a good choice?
Or can you use a normal combi boiler and simply not use the heating
part, or maybe just have a towel rail if it needs a minimum load.
Or maybe time to install a full radiator system. What's the current
opinion on rad location; under window or other wall?
Can you put a heater/combi on a stud wall? I think I read that they
might be noisy in this situation.
Thanks for reading and any comments.

On Tuesday, 3 May 2016 22:50:12 UTC+1, Grumps wrote:
I've just moved into a house that has hot water supplied by an electric
immersion heater. The small cold water tank is the top part of the hot
water cylinder. When running a bath the cold tank seems to empty far
quicker than it can refill from the mains. Consequently the hot water
starts to splurge out; still hot though.

The cold mains should be sufficient to fill faster than the hot draw-off - check the stopcock or ballcock. Or just only open the bathtap halfway.

Combi boilers or gas instantaneous water heaters are adequate for showers but not usually for filling a bath very quickly. Gas pipe size depends on kW heat input to the appliance, length of pipe and number of bends. 22mm is usual but you might need 28mm.

Fairly straightforward to use a combi boiler with the instant hot water for the shower, and the heating side S-plus plan to a vented indirect cylinder for a bath, and radiators if required.

Owain

On Tuesday, 3 May 2016 22:50:12 UTC+1, Grumps wrote:
Hi All
I've just moved into a house that has hot water supplied by an electric
immersion heater. The small cold water tank is the top part of the hot
water cylinder. When running a bath the cold tank seems to empty far
quicker than it can refill from the mains. Consequently the hot water
starts to splurge out; still hot though.

only way to fix that is a bigger HW cylinder. Or just live with wartime baths.

Taking a shower which is fed from these tanks has woefully low pressure
and a piddly experience. I could put a pump on this but a shower would
then be short but sweet! And I could replace the cylinder with a loft
cold tank and standard hot water cylinder. There is also an electric
shower (10kW), but this too is rather poor.
So, I was considering a gas powered water heater to provide "continuous"
hot water at mains pressure. Several models seem to be available at the
£450 price point that have flow rates from 10 to 16 l/min.

but wouldn't solve the issue of low mains water flow. I'd look at aeration or pulsejet shower heads first, they'd entail far less cost & work than anything else.

The central
heating is by warm air. Don't know how efficient these systems are.
My questions are (sorry, there are lots):
Do you need special gas pipework (wider) for these gas water heaters? I

depends what you have now, but generally instant HW does mean higher power

couldn't find any reference to this in the installation instructions (or
didn't know what to look for). I will not be fitting it myself.
Are the following brands any good: Ariston, Rinnai, Main, Vokera. Any
others that may be a good choice?

Vaillant & Worcester Bosch are the top 2, the rest a fair way behind on reliability

Or can you use a normal combi boiler and simply not use the heating
part, or maybe just have a towel rail if it needs a minimum load.
Or maybe time to install a full radiator system.

is the warm air system problematic?

What's the current
opinion on rad location; under window or other wall?

both work fine

Can you put a heater/combi on a stud wall? I think I read that they
might be noisy in this situation.
Thanks for reading and any comments.

If you did the combi would use the wall as a sounding board.


NT

On 03/05/2016 23:29, wrote:
On Tuesday, 3 May 2016 22:50:12 UTC+1, Grumps wrote:
Hi All
I've just moved into a house that has hot water supplied by an electric
immersion heater. The small cold water tank is the top part of the hot
water cylinder. When running a bath the cold tank seems to empty far
quicker than it can refill from the mains. Consequently the hot water
starts to splurge out; still hot though.

only way to fix that is a bigger HW cylinder. Or just live with wartime baths.

Taking a shower which is fed from these tanks has woefully low pressure
and a piddly experience. I could put a pump on this but a shower would
then be short but sweet! And I could replace the cylinder with a loft
cold tank and standard hot water cylinder. There is also an electric
shower (10kW), but this too is rather poor.
So, I was considering a gas powered water heater to provide "continuous"
hot water at mains pressure. Several models seem to be available at the
£450 price point that have flow rates from 10 to 16 l/min.

but wouldn't solve the issue of low mains water flow. I'd look at aeration or pulsejet shower heads first, they'd entail far less cost & work than anything else.

The mains pressure seems fine in the kitchen and upstairs bathroom sink.
The bath runs from stored hot+cold and hasn't sufficient head for a
decent shower (it's a shower mixer tap thing).

The central
heating is by warm air. Don't know how efficient these systems are.
My questions are (sorry, there are lots):
Do you need special gas pipework (wider) for these gas water heaters? I

depends what you have now, but generally instant HW does mean higher power

couldn't find any reference to this in the installation instructions (or
didn't know what to look for). I will not be fitting it myself.
Are the following brands any good: Ariston, Rinnai, Main, Vokera. Any
others that may be a good choice?

Vaillant & Worcester Bosch are the top 2, the rest a fair way behind on reliability

I'll check them out. Ta.

Or can you use a normal combi boiler and simply not use the heating
part, or maybe just have a towel rail if it needs a minimum load.
Or maybe time to install a full radiator system.

is the warm air system problematic?

No. It's fine. Quick to warm up.

What's the current
opinion on rad location; under window or other wall?

both work fine

Can you put a heater/combi on a stud wall? I think I read that they
might be noisy in this situation.
Thanks for reading and any comments.

If you did the combi would use the wall as a sounding board.

OK. Outside wall it will be if I go that route.
Ta.

On 03/05/2016 22:50, Grumps wrote:

I've just moved into a house that has hot water supplied by an electric
immersion heater. The small cold water tank is the top part of the hot
water cylinder. When running a bath the cold tank seems to empty far
quicker than it can refill from the mains. Consequently the hot water
starts to splurge out; still hot though.

Those combined cylinders and cisterns are rarely satisfactory.

Taking a shower which is fed from these tanks has woefully low pressure
and a piddly experience. I could put a pump on this but a shower would
then be short but sweet! And I could replace the cylinder with a loft
cold tank and standard hot water cylinder. There is also an electric
shower (10kW), but this too is rather poor.

Poor for different reasons though... It would be a worthwhile exercise
to measure the cold mains flow at the best tap (kitchen perhaps) to work
out what kind of flow rate you can get. You need at least 15 lpm before
being able to get decent performance out of any system that depends on
mains flow rate (i.e. combi, multipoint, heatbank, unvented cylinder etc)

So, I was considering a gas powered water heater to provide "continuous"
hot water at mains pressure. Several models seem to be available at the
£450 price point that have flow rates from 10 to 16 l/min.

The flow rate comes down to power - 24kW will give you the lower figure,
and you will need 35kW+ for the latter.

The central
heating is by warm air. Don't know how efficient these systems are.

They have pros and cons, but if installed and maintained properly can be
good.

My questions are (sorry, there are lots):

Do you need special gas pipework (wider) for these gas water heaters?

Instant water heaters need power to work (if you want something more
impressive than an electric shower!) So that typically means at least
some of the pipe run will need to be in at least 22mm copper pipe
(unless the boiler is very close to the meter). Higher powers, and
longer pipe runs may even dictate wider.

I
couldn't find any reference to this in the installation instructions (or
didn't know what to look for).

Gas pipe sizing needs to be worked out for each installation normally,
although there are various rules of thumb that the less clued up fitters
will use in place of doing the actual sums.

BS 6891 Annex A ("Installation of low pressure gas pipework of up to 35
mm (R1¼) in domestic premises (2nd family gas)" will give you the basics
(you may be able to view a copy online using a library card number)

In summary though it comes down to find out the flow rate required (in
cubic metres per hour), work out the effective pipe run in meters (where
an elbow counts as 0.5m, and a swept bend 0.3m), Then look up in table
the maximum length of pipe of your chosen size that can discharge at
least the required amount of gas.

To give you an idea, a 35kW boiler will suck just over 3m^3/h

(multiply the power by around 0.09 to convert to m^3/h):

http://wiki.diyfaq.org.uk/index.php/Gas_units

At that rate, the longest run of 22mm pipe you could cope with before
dropping too much pressure would be around 16 odd metres.

I will not be fitting it myself.
Are the following brands any good: Ariston, Rinnai, Main, Vokera.

If looking at multipoints specifically, there is less choice that with
combis and other boilers.

Any
others that may be a good choice?

Or can you use a normal combi boiler and simply not use the heating
part, or maybe just have a towel rail if it needs a minimum load.

You would need a minimal primary circuit typically (the combi normally
diverts this through one side of a plate heat exchanger when heating the
water (although there are a few exceptions that use the main HE for DHW
heating). You could also use a combi to heat a normal hot water cylinder
- using the mains pressure feed for a shower, and the tank for the rest
of the plumbing.

Or maybe time to install a full radiator system. What's the current
opinion on rad location; under window or other wall?

Either... or under floor heating.

Can you put a heater/combi on a stud wall?

You can - assuming the fluing options allow for sufficient run to an
outside wall. The wall needs to be non combustible as well (which
plasterboard normally is)

I think I read that they
might be noisy in this situation.

Slightly more perhaps - but with a decent quiet boiler, not dramatically
so. A solid wall is easier though - especially for fixing.

Thanks for reading and any comments.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On Wednesday, 4 May 2016 03:04:57 UTC+1, John Rumm wrote:
Gas pipe sizing needs to be worked out for each installation normally,
although there are various rules of thumb that the less clued up fitters
will use in place of doing the actual sums.

"The boiler's got a 15mm inlet so a 15mm pipe will be okay, regardless of kW or length"

Owain

wrote:
On Wednesday, 4 May 2016 03:04:57 UTC+1, John Rumm wrote:
Gas pipe sizing needs to be worked out for each installation normally,
although there are various rules of thumb that the less clued up fitters
will use in place of doing the actual sums.

"The boiler's got a 15mm inlet so a 15mm pipe will be okay, regardless of kW or length"

It's not clear whether you're quoting a "less clued up fitter" or
contradicting John.

Tim

--
Trolls AND TROLL FEEDERS all go in my kill file

In article ,
Tim+ writes:
wrote:
On Wednesday, 4 May 2016 03:04:57 UTC+1, John Rumm wrote:
Gas pipe sizing needs to be worked out for each installation normally,
although there are various rules of thumb that the less clued up fitters
will use in place of doing the actual sums.

"The boiler's got a 15mm inlet so a 15mm pipe will be okay, regardless of kW or length"

It's not clear whether you're quoting a "less clued up fitter" or
contradicting John.

But just to be clear, it's not true.

My Keston has a 15mm gas inlet fitting, but needs 28mm most of the
way from the gas meter due to being at other end of the house.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On 5/4/2016 8:32 AM, Andrew Gabriel wrote:
In article ,
Tim+ writes:
wrote:
On Wednesday, 4 May 2016 03:04:57 UTC+1, John Rumm wrote:
Gas pipe sizing needs to be worked out for each installation normally,
although there are various rules of thumb that the less clued up fitters
will use in place of doing the actual sums.

"The boiler's got a 15mm inlet so a 15mm pipe will be okay, regardless of kW or length"

It's not clear whether you're quoting a "less clued up fitter" or
contradicting John.

But just to be clear, it's not true.

+1


My Keston has a 15mm gas inlet fitting, but needs 28mm most of the
way from the gas meter due to being at other end of the house.

On 04/05/2016 06:38, wrote:
On Wednesday, 4 May 2016 03:04:57 UTC+1, John Rumm wrote:
Gas pipe sizing needs to be worked out for each installation normally,
although there are various rules of thumb that the less clued up fitters
will use in place of doing the actual sums.

"The boiler's got a 15mm inlet so a 15mm pipe will be okay, regardless of kW or length"

Yup, that would be one!

(I have also met the "must be 22mm!" - for a 15kW boiler 2m from the meter)


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

In article ,
John Rumm writes:
On 03/05/2016 22:50, Grumps wrote:

I've just moved into a house that has hot water supplied by an electric
immersion heater. The small cold water tank is the top part of the hot
water cylinder. When running a bath the cold tank seems to empty far
quicker than it can refill from the mains. Consequently the hot water
starts to splurge out; still hot though.

Those combined cylinders and cisterns are rarely satisfactory.

They have a common fault in hard water areas. The pipe from the
top cistern to the inlet at bottom of the hot water tank often runs
through the hot water tank. That heats the cold water as it flows
down that pipe, and over the years, scale builds up in that pipe
and restricts it. If your cistern is still full when hot water
stops flowing, it's a good pointer to this having happened (or
something else restricting flow in that pipe - remains of a drowned
mouse or similar).

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

Strip and check your ball float valve hasnt got a piece of crud in the internal "jet" before launching into capital expenditure.

wrote in
:

Strip and check your ball float valve hasnt got a piece of crud in the
internal "jet" before launching into capital expenditure.


+1 - it may even have the wrong size nozzle for the pressure rating.

On Tuesday, 3 May 2016 22:50:12 UTC+1, Grumps wrote:
Hi All
I've just moved into a house that has hot water supplied by an electric
immersion heater. The small cold water tank is the top part of the hot
water cylinder. When running a bath the cold tank seems to empty far
quicker than it can refill from the mains. Consequently the hot water
starts to splurge out; still hot though.
Taking a shower which is fed from these tanks has woefully low pressure
and a piddly experience. I could put a pump on this but a shower would
then be short but sweet! And I could replace the cylinder with a loft
cold tank and standard hot water cylinder. There is also an electric
shower (10kW), but this too is rather poor.
So, I was considering a gas powered water heater to provide "continuous"
hot water at mains pressure. Several models seem to be available at the
£450 price point that have flow rates from 10 to 16 l/min. The central
heating is by warm air. Don't know how efficient these systems are.
My questions are (sorry, there are lots):
Do you need special gas pipework (wider) for these gas water heaters? I
couldn't find any reference to this in the installation instructions (or
didn't know what to look for). I will not be fitting it myself.
Are the following brands any good: Ariston, Rinnai, Main, Vokera. Any
others that may be a good choice?
Or can you use a normal combi boiler and simply not use the heating
part, or maybe just have a towel rail if it needs a minimum load.
Or maybe time to install a full radiator system. What's the current
opinion on rad location; under window or other wall?
Can you put a heater/combi on a stud wall? I think I read that they
might be noisy in this situation.
Thanks for reading and any comments.

Think about it.
The limitation you have is due to water not filling the tank fast enough.
If you get a gas instantaneous heater it with be fed from the same source.
Ergo it will be no faster though the pressure may be higher (for showering)..

So, you need to look into the cause of the slow mains water.
Look for closed valves.
Look for those silly ball valves that only have a very small water passage inside.
If the mains pressure is low, you might be able to change the float valve (jet)in the header tank to one of lower pressure (ie a bigger hole)

The istallation you describe dates from the 1960s
You may find your incoming mains pipe is filled with crud.This means the pressure will still be there but not the flow.
If this is the case, the only solution is to replace it.
Things will gradually get worse.

So the first thing is to determine if you have low mains pressure or the incoming pipe is partially blocked/valves obstructing flow.
There's no point spending any money until you have found out which and dealt with the matter.
When you have fixed this problem, you'll likely find the existing installation works perfectly well.

On 04/05/2016 07:56, harry wrote:
On Tuesday, 3 May 2016 22:50:12 UTC+1, Grumps wrote:
Hi All
I've just moved into a house that has hot water supplied by an electric
immersion heater. The small cold water tank is the top part of the hot
water cylinder. When running a bath the cold tank seems to empty far
quicker than it can refill from the mains. Consequently the hot water
starts to splurge out; still hot though.

Think about it.
The limitation you have is due to water not filling the tank fast enough.
If you get a gas instantaneous heater it with be fed from the same source.
Ergo it will be no faster though the pressure may be higher (for showering).

One can't say that with any certainty. It could just be a poor or
inadequate ball valve that's limiting flow rate - the combi (or
whatever) is not going to be fed from the same ball valve.

Also running a bath (though low flow resistance taps and pipework), may
still permit a flow rate higher than that which the mains can supply -
that does not automatically mean that a lower mains driven flow rate
would necessarily be too low.

(i.e. say the main can deliver 20 lpm, and the current setup can fill
the bath at 30 lpm. Swapping to a combi which can deliver 15 lpm will
result in slower bath fills, but the combi will still have a more than
adequate flow of water from the mains)

So, you need to look into the cause of the slow mains water.
Look for closed valves.
Look for those silly ball valves that only have a very small water passage inside.

or one fitted with a "high pressure" flow restriction.

If the mains pressure is low, you might be able to change the float valve (jet)in the header tank to one of lower pressure (ie a bigger hole)

Indeed.

The istallation you describe dates from the 1960s
You may find your incoming mains pipe is filled with crud.This means the pressure will still be there but not the flow.
If this is the case, the only solution is to replace it.
Things will gradually get worse.

Its quite likely only a 15mm pipe as well...

So the first thing is to determine if you have low mains pressure or the incoming pipe is partially blocked/valves obstructing flow.
There's no point spending any money until you have found out which and dealt with the matter.
When you have fixed this problem, you'll likely find the existing installation works perfectly well.

Pressure at the shower will still be crap.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 04/05/2016 12:06, John Rumm wrote:
On 04/05/2016 07:56, harry wrote:
On Tuesday, 3 May 2016 22:50:12 UTC+1, Grumps wrote:
Hi All
I've just moved into a house that has hot water supplied by an electric
immersion heater. The small cold water tank is the top part of the hot
water cylinder. When running a bath the cold tank seems to empty far
quicker than it can refill from the mains. Consequently the hot water
starts to splurge out; still hot though.

Think about it.
The limitation you have is due to water not filling the tank fast enough.
If you get a gas instantaneous heater it with be fed from the same
source.
Ergo it will be no faster though the pressure may be higher (for
showering).

One can't say that with any certainty. It could just be a poor or
inadequate ball valve that's limiting flow rate - the combi (or
whatever) is not going to be fed from the same ball valve.

Also running a bath (though low flow resistance taps and pipework), may
still permit a flow rate higher than that which the mains can supply -
that does not automatically mean that a lower mains driven flow rate
would necessarily be too low.

(i.e. say the main can deliver 20 lpm, and the current setup can fill
the bath at 30 lpm. Swapping to a combi which can deliver 15 lpm will
result in slower bath fills, but the combi will still have a more than
adequate flow of water from the mains)

So, you need to look into the cause of the slow mains water.
Look for closed valves.
Look for those silly ball valves that only have a very small water
passage inside.

or one fitted with a "high pressure" flow restriction.

If the mains pressure is low, you might be able to change the float
valve (jet)in the header tank to one of lower pressure (ie a bigger hole)

Indeed.

The istallation you describe dates from the 1960s
You may find your incoming mains pipe is filled with crud.This means
the pressure will still be there but not the flow.
If this is the case, the only solution is to replace it.
Things will gradually get worse.

Its quite likely only a 15mm pipe as well...

So the first thing is to determine if you have low mains pressure or
the incoming pipe is partially blocked/valves obstructing flow.
There's no point spending any money until you have found out which and
dealt with the matter.
When you have fixed this problem, you'll likely find the existing
installation works perfectly well.

Pressure at the shower will still be crap.

Just a little extra info.
I was talking with my neighbour and told him about the splurging hot
water. He said his was the same. Was always like that from new!

I measured the flow rate from the kitchen cold tap (mains). I get a
better shower from that tap spraying all over the place than I do from
the one in the bathroom! It measured about 31 l/min. The bathroom cold
tap (also from mains) measured about 22 l/min.

So I'm still inclined to replace the hot/cold tank with an instantaneous
gas water heater.

On 06/05/2016 20:21, Grumps wrote:
On 04/05/2016 12:06, John Rumm wrote:
On 04/05/2016 07:56, harry wrote:
On Tuesday, 3 May 2016 22:50:12 UTC+1, Grumps wrote:
Hi All
I've just moved into a house that has hot water supplied by an electric
immersion heater. The small cold water tank is the top part of the hot
water cylinder. When running a bath the cold tank seems to empty far
quicker than it can refill from the mains. Consequently the hot water
starts to splurge out; still hot though.

Think about it.
The limitation you have is due to water not filling the tank fast
enough.
If you get a gas instantaneous heater it with be fed from the same
source.
Ergo it will be no faster though the pressure may be higher (for
showering).

One can't say that with any certainty. It could just be a poor or
inadequate ball valve that's limiting flow rate - the combi (or
whatever) is not going to be fed from the same ball valve.

Also running a bath (though low flow resistance taps and pipework), may
still permit a flow rate higher than that which the mains can supply -
that does not automatically mean that a lower mains driven flow rate
would necessarily be too low.

(i.e. say the main can deliver 20 lpm, and the current setup can fill
the bath at 30 lpm. Swapping to a combi which can deliver 15 lpm will
result in slower bath fills, but the combi will still have a more than
adequate flow of water from the mains)

So, you need to look into the cause of the slow mains water.
Look for closed valves.
Look for those silly ball valves that only have a very small water
passage inside.

or one fitted with a "high pressure" flow restriction.

If the mains pressure is low, you might be able to change the float
valve (jet)in the header tank to one of lower pressure (ie a bigger
hole)

Indeed.

The istallation you describe dates from the 1960s
You may find your incoming mains pipe is filled with crud.This means
the pressure will still be there but not the flow.
If this is the case, the only solution is to replace it.
Things will gradually get worse.

Its quite likely only a 15mm pipe as well...

So the first thing is to determine if you have low mains pressure or
the incoming pipe is partially blocked/valves obstructing flow.
There's no point spending any money until you have found out which and
dealt with the matter.
When you have fixed this problem, you'll likely find the existing
installation works perfectly well.

Pressure at the shower will still be crap.

Just a little extra info.
I was talking with my neighbour and told him about the splurging hot
water. He said his was the same. Was always like that from new!

I measured the flow rate from the kitchen cold tap (mains). I get a
better shower from that tap spraying all over the place than I do from
the one in the bathroom! It measured about 31 l/min. The bathroom cold
tap (also from mains) measured about 22 l/min.

31 lpm is a good basis for any mains pressure system.

So I'm still inclined to replace the hot/cold tank with an instantaneous
gas water heater.

It will work, but you may find the flow rate for bath filling will be a
bit disappointing. (i.e. probably 15 lpm at final temperature - no scope
for adding extra cold at the same time). But, its simple and relatively
cheap. A simple gas system boiler and unvented cylinder would give much
better results - but take more space and cost a bit more.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On Sunday, 8 May 2016 03:43:29 UTC+1, John Rumm wrote:
On 06/05/2016 20:21, Grumps wrote:
On 04/05/2016 12:06, John Rumm wrote:
On 04/05/2016 07:56, harry wrote:
On Tuesday, 3 May 2016 22:50:12 UTC+1, Grumps wrote:
Hi All
I've just moved into a house that has hot water supplied by an electric
immersion heater. The small cold water tank is the top part of the hot
water cylinder. When running a bath the cold tank seems to empty far
quicker than it can refill from the mains. Consequently the hot water
starts to splurge out; still hot though.

Think about it.
The limitation you have is due to water not filling the tank fast
enough.
If you get a gas instantaneous heater it with be fed from the same
source.
Ergo it will be no faster though the pressure may be higher (for
showering).

One can't say that with any certainty. It could just be a poor or
inadequate ball valve that's limiting flow rate - the combi (or
whatever) is not going to be fed from the same ball valve.

Also running a bath (though low flow resistance taps and pipework), may
still permit a flow rate higher than that which the mains can supply -
that does not automatically mean that a lower mains driven flow rate
would necessarily be too low.

(i.e. say the main can deliver 20 lpm, and the current setup can fill
the bath at 30 lpm. Swapping to a combi which can deliver 15 lpm will
result in slower bath fills, but the combi will still have a more than
adequate flow of water from the mains)

So, you need to look into the cause of the slow mains water.
Look for closed valves.
Look for those silly ball valves that only have a very small water
passage inside.

or one fitted with a "high pressure" flow restriction.

If the mains pressure is low, you might be able to change the float
valve (jet)in the header tank to one of lower pressure (ie a bigger
hole)

Indeed.

The istallation you describe dates from the 1960s
You may find your incoming mains pipe is filled with crud.This means
the pressure will still be there but not the flow.
If this is the case, the only solution is to replace it.
Things will gradually get worse.

Its quite likely only a 15mm pipe as well...

So the first thing is to determine if you have low mains pressure or
the incoming pipe is partially blocked/valves obstructing flow.
There's no point spending any money until you have found out which and
dealt with the matter.
When you have fixed this problem, you'll likely find the existing
installation works perfectly well.

Pressure at the shower will still be crap.

Just a little extra info.
I was talking with my neighbour and told him about the splurging hot
water. He said his was the same. Was always like that from new!

I measured the flow rate from the kitchen cold tap (mains). I get a
better shower from that tap spraying all over the place than I do from
the one in the bathroom! It measured about 31 l/min. The bathroom cold
tap (also from mains) measured about 22 l/min.

31 lpm is a good basis for any mains pressure system.

So I'm still inclined to replace the hot/cold tank with an instantaneous
gas water heater.

It will work, but you may find the flow rate for bath filling will be a
bit disappointing. (i.e. probably 15 lpm at final temperature - no scope
for adding extra cold at the same time). But, its simple and relatively
cheap. A simple gas system boiler and unvented cylinder would give much
better results - but take more space and cost a bit more.


--
Cheers,

John.

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The water will still only come out as fast as it goes in.

On 08/05/2016 03:43, John Rumm wrote:
On 06/05/2016 20:21, Grumps wrote:
On 04/05/2016 12:06, John Rumm wrote:
On 04/05/2016 07:56, harry wrote:
On Tuesday, 3 May 2016 22:50:12 UTC+1, Grumps wrote:
Hi All
I've just moved into a house that has hot water supplied by an
electric
immersion heater. The small cold water tank is the top part of the hot
water cylinder. When running a bath the cold tank seems to empty far
quicker than it can refill from the mains. Consequently the hot water
starts to splurge out; still hot though.

Think about it.
The limitation you have is due to water not filling the tank fast
enough.
If you get a gas instantaneous heater it with be fed from the same
source.
Ergo it will be no faster though the pressure may be higher (for
showering).

One can't say that with any certainty. It could just be a poor or
inadequate ball valve that's limiting flow rate - the combi (or
whatever) is not going to be fed from the same ball valve.

Also running a bath (though low flow resistance taps and pipework), may
still permit a flow rate higher than that which the mains can supply -
that does not automatically mean that a lower mains driven flow rate
would necessarily be too low.

(i.e. say the main can deliver 20 lpm, and the current setup can fill
the bath at 30 lpm. Swapping to a combi which can deliver 15 lpm will
result in slower bath fills, but the combi will still have a more than
adequate flow of water from the mains)

So, you need to look into the cause of the slow mains water.
Look for closed valves.
Look for those silly ball valves that only have a very small water
passage inside.

or one fitted with a "high pressure" flow restriction.

If the mains pressure is low, you might be able to change the float
valve (jet)in the header tank to one of lower pressure (ie a bigger
hole)

Indeed.

The istallation you describe dates from the 1960s
You may find your incoming mains pipe is filled with crud.This means
the pressure will still be there but not the flow.
If this is the case, the only solution is to replace it.
Things will gradually get worse.

Its quite likely only a 15mm pipe as well...

So the first thing is to determine if you have low mains pressure or
the incoming pipe is partially blocked/valves obstructing flow.
There's no point spending any money until you have found out which and
dealt with the matter.
When you have fixed this problem, you'll likely find the existing
installation works perfectly well.

Pressure at the shower will still be crap.

Just a little extra info.
I was talking with my neighbour and told him about the splurging hot
water. He said his was the same. Was always like that from new!

I measured the flow rate from the kitchen cold tap (mains). I get a
better shower from that tap spraying all over the place than I do from
the one in the bathroom! It measured about 31 l/min. The bathroom cold
tap (also from mains) measured about 22 l/min.

31 lpm is a good basis for any mains pressure system.

So I'm still inclined to replace the hot/cold tank with an instantaneous
gas water heater.

It will work, but you may find the flow rate for bath filling will be a
bit disappointing. (i.e. probably 15 lpm at final temperature - no scope
for adding extra cold at the same time). But, its simple and relatively
cheap. A simple gas system boiler and unvented cylinder would give much
better results - but take more space and cost a bit more.

Thanks.
For comparison, I have another house which has a loft water tank and
vented cylinder. In the bathroom the bath single-lever mixer tap can
deliver the following flow rates (all pipework seems to be 22mm):
Cold(from loft):11 l/min, Hot:12 l/min, Mixed:15 l/min
Filling a bath does take a bit of time, but it's not too bad.

So, (yeah I know I'm banging on about gas water heaters) an
instantaneous water heater could provide a flow of 12 l/min (delta T
35C). I was also planning on using a thermostatic mixer tap with shower
attachment. The hot would come from the heater, the cold would be mains.
With a winter min cold temp of 5C (apparently) then theoretically the
heater should be able to provide a 40C shower at 12 l/min (larger values
would be possible at a higher heater cost).

Haven't looked at unvented cylinders yet.