I want to fit a new combi boiler for my office, and I want to do as much
work as possible myself, just getting the final commissioning done by a
Corgi.

There is a (condemned) floor standing boiler at present, and I want to
replace this with a wall-hung combi immediately above, to minimise the
pipework changes. Hot water is currently from an electric water heater which
will be discarded.

The current boiler is about 20 KW and heating is adequate. New combi needs
only to supply a sink for washing up, but I did think of adding a shower
cubicle some time in the future. Office is ground floor with a handful of
rooms. Cellar underneath.

I originally thought of a Potterton 24, but I am now more inclined to a
Vaillant TurboMax Plus 28, even though this is 25% more expensive.
Obviously, this is overkill for the heating, but I want to leave a bit in
reserve for the shower if it ever gets fitted. Anybody any
suggestions/comments, please?

One reason for the Vaillant is that it takes a 15mm gas supply whereas the
Potterton takes 22mm. The boiler is quite close to the meter but the gas
pipe is only 15mm. Does it matter what the inlet pipe to the boiler is? I
was told by a fitter that I needed a new 22mm pipe for a combi, but he never
bothered to look where the meter was and how close it is. The max gas flow
needed is about 3.5cubic metres/hr for the Potterton and I assume it must be
similar for the Vaillant, so I am a bit surprised that the Vaillant takes a
15 mm gas pipe. Looking at the cda calculator, the 15 mm pipe would need a
pressure differential of 2mbar to deliver this flow over a length of 6m,
whereas only 1 mbar is acceptable. Why is the acceptable pressure drop so
low? The burners operate at between 12 mbar and 2 mbar. If the pressure at
the meter is 20 mbar, at peak flow, the pressure at the boiler reduces to 18
mbar. Why is that not okay? Do I definitely need to rerun the pipework in
22mm?

The present system is gravity fed with a pressure of about 0.25 bar. I would
be right in thinking I need to pressure test the existing pipe-work? What is
the best way of doing this?

I want to flush out the old pipework with Fernox sludge remover/cleaner. Am
I right in thinking that I might as well do that with the old boiler in
place? That avoids washing all the old crud through the new boiler. Do I
need to flush out again with the new boiler fitted, as well? The Fernox is
about 15 quid a bottle, so I don't want to (literally) throw money down the
drain.

What is the best way of getting inhibitor into the new sealed system? Do I
just use the filling loop? Presumably BEFORE pressuring the system with
water? And can you just pour it in with a funnel?

Fitting the new flue sounds interesting. The boiler is mounted on an
exterior wall, so a core cutter bit should do the trick, mounted on a big
drill. How do you fill in around the flue once it is fitted? Just sand and
cement?

Sorry to ask so many questions, but I want to get this completely clear in
my mind before starting.

Thanks

Geoff

"GB" wrote in message
...

I want to fit a new combi boiler for my office, and I want to do as much
work as possible myself, just getting the final commissioning done by a
Corgi.

There is a (condemned) floor standing boiler at present, and I want to
replace this with a wall-hung combi immediately above, to minimise the
pipework changes. Hot water is currently from an electric water heater
which
will be discarded.

The current boiler is about 20 KW and heating is adequate. New combi needs
only to supply a sink for washing up, but I did think of adding a shower
cubicle some time in the future. Office is ground floor with a handful of
rooms. Cellar underneath.

I originally thought of a Potterton 24, but I am now more inclined to a
Vaillant TurboMax Plus 28, even though this is 25% more expensive.
Obviously, this is overkill for the heating, but I want to leave a bit in
reserve for the shower if it ever gets fitted. Anybody any
suggestions/comments, please?

One reason for the Vaillant is that it takes a 15mm gas supply whereas the
Potterton takes 22mm. The boiler is quite close to the meter but the gas
pipe is only 15mm. Does it matter what the inlet pipe to the boiler is?

The Vaillant is a good boiler. Get the smallest combi you can and run a
22mm gas pipe right up to it.

Do I definitely need to rerun the pipework in 22mm?

yes.

The present system is gravity fed with a pressure of about 0.25 bar. I
would
be right in thinking I need to pressure test the existing pipe-work? What
is
the best way of doing this?

There are special kits to do this. But you could connect up the combi,
pressurise and look around the system for leaks. Any leaks fix them.

I want to flush out the old pipework with Fernox sludge remover/cleaner.
Am
I right in thinking that I might as well do that with the old boiler in
place? That avoids washing all the old crud through the new boiler.

yes.

Do I need to flush out again with the new boiler fitted, as well? The
Fernox is
about 15 quid a bottle, so I don't want to (literally) throw money down
the
drain.

No need to use fernox again, just a flush out with fresh water.

What is the best way of getting inhibitor
into the new sealed system? Do I
just use the filling loop? Presumably BEFORE
pressuring the system with
water? And can you just pour it in with a funnel?

Install a filling point of 22mm pipe. Have a compression cap on the end and
use a funnel.

Fitting the new flue sounds interesting. The boiler is mounted on an
exterior wall, so a core cutter bit should do the trick, mounted on a big
drill. How do you fill in around the flue once it is fitted? Just sand and
cement?

Yes. Using the right sized drill will mean the flue will fit snugly.

The blow-off pipe should be taken to outside at low level, with an elbow
pointing to the wall. It should be copper.

Sorry to ask so many questions, but
I want to get this completely clear in
my mind before starting.



---
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On Sun, 7 Sep 2003 12:52:18 +0100, "GB"
wrote:

I want to fit a new combi boiler for my office, and I want to do as much
work as possible myself, just getting the final commissioning done by a
Corgi.

There is a (condemned) floor standing boiler at present, and I want to
replace this with a wall-hung combi immediately above, to minimise the
pipework changes. Hot water is currently from an electric water heater which
will be discarded.

The current boiler is about 20 KW and heating is adequate. New combi needs
only to supply a sink for washing up, but I did think of adding a shower
cubicle some time in the future. Office is ground floor with a handful of
rooms. Cellar underneath.

I originally thought of a Potterton 24, but I am now more inclined to a
Vaillant TurboMax Plus 28, even though this is 25% more expensive.
Obviously, this is overkill for the heating, but I want to leave a bit in
reserve for the shower if it ever gets fitted. Anybody any
suggestions/comments, please?

How about a condensing version such as the EcoMax?

One reason for the Vaillant is that it takes a 15mm gas supply whereas the
Potterton takes 22mm. The boiler is quite close to the meter but the gas
pipe is only 15mm. Does it matter what the inlet pipe to the boiler is?

The issue is the flow rate that the boiler requires and the pressure
drop allowed. As you deduced from the CDA site, these can easily be
worked out.

It is quite common, for convenience to run the last metre or so of
pipe at the boiler in 15mm even if most of the run is 22mm. It's the
overall behaviour that matters. Often boilers are fitted with an
isolating cock with 1/2" BSP inlet and this goes more naturally with
15mm tube for a short run.

I
was told by a fitter that I needed a new 22mm pipe for a combi, but he never
bothered to look where the meter was and how close it is.

So he's flying by the seat of his pants and assuming characteristics
of the installation. It depends on the required gas rate and the run
length of pipe.

The max gas flow
needed is about 3.5cubic metres/hr for the Potterton and I assume it must be
similar for the Vaillant, so I am a bit surprised that the Vaillant takes a
15 mm gas pipe. Looking at the cda calculator, the 15 mm pipe would need a
pressure differential of 2mbar to deliver this flow over a length of 6m,
whereas only 1 mbar is acceptable. Why is the acceptable pressure drop so
low? The burners operate at between 12 mbar and 2 mbar. If the pressure at
the meter is 20 mbar, at peak flow, the pressure at the boiler reduces to 18
mbar. Why is that not okay? Do I definitely need to rerun the pipework in
22mm?

The CDA site information is based on the British Standard for doing
this. From what you are saying, you probably do need to run in 22mm
apart from possibly the last short piece to the boiler.


The present system is gravity fed with a pressure of about 0.25 bar. I would
be right in thinking I need to pressure test the existing pipe-work? What is
the best way of doing this?

It wouldn't hurt, although remember that you are only going up to 3bar
maximum which is the same or less than the cold water mains.

The most likely problems are going to be that the radiator valves will
weep at the seals. I had one which did this and decided for the
sake of completeness to change all of them. The easiest test is
simply to do the conversion to sealed operation, capping off the
boiler connections and check for pressure loss on the gauge.
If you think that there might be problems, run the system after
installing for a few weeks before adding the inhibitor in case you
need to drain and fix.



I want to flush out the old pipework with Fernox sludge remover/cleaner. Am
I right in thinking that I might as well do that with the old boiler in
place?

That's what I did a couple of weeks before ripping out the old boiler.

That avoids washing all the old crud through the new boiler.

It's a good idea to put a strainer on the return to the boiler anyway.

Do I
need to flush out again with the new boiler fitted, as well?

I did an initial flush round with remover and the old boiler, then
switched boilers putting lever ball valves on either side of it (there
is a pressure relief valve in the boiler for safety). I added in the
sealed system components and then using the filling loop flushed at
each radiator. THis drives the crud out at each radiator point and
I flushed through both valves and took the radiator outside for a good
pressure washing.
I filled and used sludge remover again before finally flushing and
filling with added inhibitor. Possibly the second go with remover
isn't necessary but £15 in the context of the system is nothing.


The Fernox is
about 15 quid a bottle, so I don't want to (literally) throw money down the
drain.

What is the best way of getting inhibitor into the new sealed system? Do I
just use the filling loop? Presumably BEFORE pressuring the system with
water? And can you just pour it in with a funnel?

You can get sludge remover and inhibitor chemicals from Fernox in gel
form which can be injected through a radiator vent - I use an empty
one, not a full one as the instructions suggest. Alternatively you
can put in a chemical introduction point by using a valve and short
piece of vertical pipe and then a funnel to introduce chemicals.



Fitting the new flue sounds interesting. The boiler is mounted on an
exterior wall, so a core cutter bit should do the trick, mounted on a big
drill. How do you fill in around the flue once it is fitted? Just sand and
cement?

Generally unless the manufacturer says otherwise.



Sorry to ask so many questions, but I want to get this completely clear in
my mind before starting.

Thanks

Geoff


..andy

To email, substitute .nospam with .gl

That avoids washing all the old crud through the new boiler.

It's a good idea to put a strainer on the return to the boiler anyway.


don't mean to hijack the thread - just a quick question:

is BES part no 7533 ok (22 mm x 22 mm compression Y in-line strainer) and
will it be ok fitted vertically below the boiler?

i know that was 2 qns - sorry!

thx
paul

Thanks IMM and Andy for those very helpful thoughts.

I will have a look at the condensing boiler, but I was put off a bit by the
price and the extra complication. Do the govt. still give a 200
contribution?

Geoff

On Sun, 7 Sep 2003 18:09:12 +0100, "Paul"
wrote:

That avoids washing all the old crud through the new boiler.

It's a good idea to put a strainer on the return to the boiler anyway.


don't mean to hijack the thread - just a quick question:

You're very welcome.

is BES part no 7533 ok (22 mm x 22 mm compression Y in-line strainer)

Yes it is.

and
will it be ok fitted vertically below the boiler?

You could, but I don't think that it's the best option.

If you look at the diagram of this fitting on the web site, the flow
of water through the fitting is from right to left. I mounted mine
horizontally as shown and then used very gentle bends made with a pipe
bender to change direction vertically into the boiler.

I have a lever ball valve on the input side of the strainer, then I go
through the boiler (which has a pressure relief valve) and there is
another lever ball valve on the flow. The filling loop is elsewhere
on the system. This arrangement means that I can turn off the
boiler, close both valves and depressurise the boiler only by undoing
the cap on the strainer. Any bits of crud in the system, which tends
to be the odd piece of copper swarf gets trapped in the strainer which
is a cylindrical stainless steel mesh behind the cap. Because of the
angle of the cap facing downwards, once crud reaches the strainer it
falls into the mesh. So all I have to do is undo and rinse it.

You could put the fitting vertically and it will work in the sense
that it will stop bits going into the boiler (this is the main point)
but the cap will be facing upwards. This means that when you undo
it, some of the bits may well fall back down the return pipe away from
the boiler. I don't think that this is a huge deal but it does make
it that bit harder to get rid of all the bits.

Having said that, if putting the strainer vertically is the only
realistic option then I think it's worth doing rather than not. If
you put in isolating valves as I did, then having a pressure relief
valve on the boiler side is a good idea, in case the boiler is
inadvertently fired up with the valves closed.




i know that was 2 qns - sorry!

No extra charge :-)





thx
paul


..andy

To email, substitute .nospam with .gl

On Sun, 7 Sep 2003 18:26:38 +0100, "GB"
wrote:

Thanks IMM and Andy for those very helpful thoughts.

I will have a look at the condensing boiler, but I was put off a bit by the
price and the extra complication. Do the govt. still give a 200
contribution?

Geoff


I'm not sure that the Big Green Boiler Scheme is running any more, but
if you compare even the SEDBUK efficiency of the two Vaillants they
are 79% vs 91%. There are arguments for and against the
measurement method used for this which is supposed to reflect
conditions in a UK house. Another approach looks at the appliance
efficiency directly under different conditions - this will also give a
10-15% difference between modern conventional and condensing
technologies. Don't be fooled by more extravagant claims regarding
condensing boilers. The figures are often stated in comparison with
much older products that had 65% efficiency or even less.

I replaced one of these old 65% efficient products about a year ago
and replaced it with a condensing model and the savings have been
pretty much as the figures would suggest.

The conventional boilers have also improved anyway, but especially
because 78% is now the minimum allowed.

A Turbomax Plus 828 at Discounted Heating is £569, an EcoMax 828 is
£928 - a difference of £359. If you amortise this across the
boiler lifetime (let's be conservative and use 15 years) then you need
to save £24 per annum in gas to make it worth it.

If you take your existing gas bill and assume that the old boiler was
probably about 60% efficient, you can work out whether this pays off.
I suspect it will.

In terms of complexity, nowadays there is not a huge difference
between non condensing and condensing system models. The main
additions are the condensate drainage arrangement which consists of a
plastic overflow pipe in most cases going to a suitable drain.
Some of the early UK manufactured condensing products did have
reliability problems, although this was largely due to poor design and
choice of materials - the condensate is acidic and this has
implications on the choices of materials.
German and Dutch manufacturers have been making them for over 15 years
and they are quite common in those countries.
I don't consider that this is a factor if you are buying a good
quality product like Vaillant. You can pretty much focus on the
energy cost difference.





..andy

To email, substitute .nospam with .gl

If you look at the diagram of this fitting on the web site, the flow
of water through the fitting is from right to left. I mounted mine
horizontally as shown and then used very gentle bends made with a pipe
bender to change direction vertically into the boiler.


Thanks andy. It's pretty easy for me to mount this horizontally so that's
what i'll do.

I have a lever ball valve on the input side of the strainer, then I go
through the boiler (which has a pressure relief valve) and there is
another lever ball valve on the flow. The filling loop is elsewhere
on the system. This arrangement means that I can turn off the
boiler, close both valves and depressurise the boiler only by undoing
the cap on the strainer. Any bits of crud in the system, which tends
to be the odd piece of copper swarf gets trapped in the strainer which
is a cylindrical stainless steel mesh behind the cap. Because of the
angle of the cap facing downwards, once crud reaches the strainer it
falls into the mesh. So all I have to do is undo and rinse it.


you've kindly described your system for me before and I've adopted some
bits.

i think it's also now wise to stick those valves on the boiler F & R - it
gives some good flexibility when i'm considering adding some old cast iron
radiators.

Having said that, if putting the strainer vertically is the only
realistic option then I think it's worth doing rather than not. If
you put in isolating valves as I did, then having a pressure relief
valve on the boiler side is a good idea, in case the boiler is
inadvertently fired up with the valves closed.

i know that was 2 qns - sorry!

No extra charge :-)

cheers