I need to put in a new CH/DHW boiler. I inherited a gas combi but the
present one is conventionally flued via an 8.5m chimney (with bends).
I am reasonably happy with a combi as long as it is sufficiently
powerful - there seem to be a number which will do the job.

The current site is bad for balanced flue access and for condensate
drain/ pressure relief valve discharge pipe. I would also like to lose
the requirement for ventilation into the room (cold draughts).

There really aren't any good sites above ground from my point of view -
obviously possible ones which usually involve destroying something else
I value and/or running flue pipes across rooms.

I would like to resite the boiler to the cellar where we have good flue
access plus good access to water and gas (though it does require a hot
water pipe to be run).

However, I am struggling with the twin issues of condensate drain and
pressure relief discharge. If I understand correctly, the condensate
could be run into a syphonic trap with a pump to periodically discharge
it. Can this discharge be connected to an external cast iron soil pipe
(which in our 1906 build carries both bath(shower) outflow and foul
water from 2nd floor toilet (incidentally Cambridge's
edwardian/victorian houses have combined surface and foul water
connections to mains drainage which would not be permitted in a modern
property)).

I suspect the answer may be no. If not we may have to dig up the
concrete outside - there is a drain inspection cover a metre or so away
but no other pipes or accessible drains nearby (nearest is 6m including
3m outside and with a doorway between).

Also what about the requirement for the discharge pipe. Will this need
a different trap and pump and pipe - the type of possible flow being v
different?

As usual any help and advice most welcome.

best wishes

Nick
----------------------------
Nick Holmes

Re combi in the basement

I have one here, the condensate goes via gravity into a small tank and
is periodically pumped out by a small electric motor, the unit's
something like 8"x8"x4". The condesate is pumped through a narrow bore,
(about 1/2" ext dia) flexible tube under the floorboards and out through
the wall into an external drain. I was a bit dubious before installation
but it's been working well for the last two years.

--
bof at bof dot me dot uk

On Fri, 02 Oct 2009 13:00:21 +0100, Nick Holmes wrote:
However, I am struggling with the twin issues of condensate drain and
pressure relief discharge. If I understand correctly, the condensate
could be run into a syphonic trap with a pump to periodically discharge
it. Can this discharge be connected to an external cast iron soil pipe
(which in our 1906 build carries both bath(shower) outflow and foul
water from 2nd floor toilet (incidentally Cambridge's
edwardian/victorian houses have combined surface and foul water
connections to mains drainage which would not be permitted in a modern
property)).

Do you mean "can" is in will it work? Or "can" as in is it legal?

Like bof, we've got a unit of about 8x4x4" with a pump which traps
condensate and pumps it up about 8' (and sideways about 10') to the cast
iron waste pipe via a narrow bit of yellow-tinted translucent tubing.
Seems to kick on for a couple of minutes a couple of times a day.

Can't comment on the legality though as a) I'm in the US and b) we have a
private septic system...

cheers

Jules

In message . com, Jules
writes

Like bof, we've got a unit of about 8x4x4" with a pump which traps
condensate and pumps it up about 8' (and sideways about 10') to the cast
iron waste pipe via a narrow bit of yellow-tinted translucent tubing.
Seems to kick on for a couple of minutes a couple of times a day.

Here the flex tube runs about 7' vertically up, then 12' under the
floorboards and is connected to a rigid plastic pipe fixed to an
exterior wall that takes the condesate another 6' to the drain.


Can't comment on the legality though as a) I'm in the US and b) we have a
private septic system...

It was installed by a CORGI here so it must be OK(!)


--
bof at bof dot me dot uk

"Nick Holmes" wrote in message
...
snip
Can this discharge be connected to an external cast iron soil pipe (which
in our 1906 build carries both bath(shower) outflow and foul water from
2nd floor toilet (incidentally Cambridge's edwardian/victorian houses have
combined surface and foul water connections to mains drainage which would
not be permitted in a modern property)).
snip

I am a bit puzzled by this - when I put a second bathroom in my 1930s house
around 2001/2 I had to run a new soil pipe to an existing manhole and I fed
both grey and black water into the same stack.

Building control were perfectly happy with this.

Is this a recent change, or does it not apply when working with older
properties?

Cheers

Dave R

"Jules" wrote in message
news
On Fri, 02 Oct 2009 13:00:21 +0100, Nick Holmes wrote:
However, I am struggling with the twin issues of condensate drain and
pressure relief discharge. If I understand correctly, the condensate
could be run into a syphonic trap with a pump to periodically discharge
it. Can this discharge be connected to an external cast iron soil pipe
(which in our 1906 build carries both bath(shower) outflow and foul
water from 2nd floor toilet (incidentally Cambridge's
edwardian/victorian houses have combined surface and foul water
connections to mains drainage which would not be permitted in a modern
property)).

Do you mean "can" is in will it work? Or "can" as in is it legal?

Like bof, we've got a unit of about 8x4x4" with a pump which traps
condensate and pumps it up about 8' (and sideways about 10') to the cast
iron waste pipe via a narrow bit of yellow-tinted translucent tubing.
Seems to kick on for a couple of minutes a couple of times a day.

I don't think I would pump it into a cast iron pipe.
Its mildly acidic and you can just dump it into a small soak away and not
risk corroding the pipe.

"David WE Roberts" wrote in message
...

"Nick Holmes" wrote in message
...
snip
Can this discharge be connected to an external cast iron soil pipe
(which in our 1906 build carries both bath(shower) outflow and foul water
from 2nd floor toilet (incidentally Cambridge's edwardian/victorian
houses have combined surface and foul water connections to mains drainage
which would not be permitted in a modern property)).
snip

I am a bit puzzled by this - when I put a second bathroom in my 1930s
house around 2001/2 I had to run a new soil pipe to an existing manhole
and I fed both grey and black water into the same stack.

Building control were perfectly happy with this.

Is this a recent change, or does it not apply when working with older
properties?

A lot of newish (less than about fifty year old) properties have separate
drains and sewers.
If you connect a sewage outlet to a drain you are in trouble and rightly so
as you are dumping untreated sewage into the rivers.
It stops the sewers from flooding when there is a storm and makes treatment
easier as there is less to treat.

David WE Roberts wrote:

"Nick Holmes" wrote in message
...
snip
Can this discharge be connected to an external cast iron soil pipe
(which in our 1906 build carries both bath(shower) outflow and foul
water from 2nd floor toilet (incidentally Cambridge's
edwardian/victorian houses have combined surface and foul water
connections to mains drainage which would not be permitted in a modern
property)).
snip

I am a bit puzzled by this - when I put a second bathroom in my 1930s
house around 2001/2 I had to run a new soil pipe to an existing manhole
and I fed both grey and black water into the same stack.

Building control were perfectly happy with this.

Is this a recent change, or does it not apply when working with older
properties?

Cheers

Dave R
More a function of your local water authority really.

But he was talking 'white' water, Rain collection.

All used water must be treated, black, brown or grey.

All rainwater ideally should end up in the subsoil or river system.

bof wrote:

Re combi in the basement

I have one here, the condensate goes via gravity into a small tank and
is periodically pumped out by a small electric motor, the unit's
something like 8"x8"x4". The condesate is pumped through a narrow bore,
(about 1/2" ext dia) flexible tube under the floorboards and out through
the wall into an external drain. I was a bit dubious before installation
but it's been working well for the last two years.



Thanks for this. What about the pressure relief discharge pipe though?

--
best wishes

Nick
----------------------------
Nick Holmes

In message , Nick Holmes
writes
bof wrote:
Re combi in the basement
I have one here, the condensate goes via gravity into a small tank
and is periodically pumped out by a small electric motor, the unit's
something like 8"x8"x4". The condesate is pumped through a narrow
bore, (about 1/2" ext dia) flexible tube under the floorboards and
out through the wall into an external drain. I was a bit dubious
before installation but it's been working well for the last two years.



Thanks for this. What about the pressure relief discharge pipe though?

There's a 15mm copper pipe goes out next to the flue, whether this is
for pressure relief or no I don't know

--
bof at bof dot me dot uk

[Type your reply here]

The Natural Philosopher wrote:
David WE Roberts wrote:

"Nick Holmes" wrote in message
...
snip
Can this discharge be connected to an external cast iron soil pipe
(which in our 1906 build carries both bath(shower) outflow and foul
water from 2nd floor toilet (incidentally Cambridge's
edwardian/victorian houses have combined surface and foul water
connections to mains drainage which would not be permitted in a modern
property)).
snip

I am a bit puzzled by this - when I put a second bathroom in my 1930s
house around 2001/2 I had to run a new soil pipe to an existing manhole
and I fed both grey and black water into the same stack.

Building control were perfectly happy with this.

Is this a recent change, or does it not apply when working with older
properties?

Cheers

Dave R
More a function of your local water authority really.

But he was talking 'white' water, Rain collection.

All used water must be treated, black, brown or grey.

All rainwater ideally should end up in the subsoil or river system.

Still confused - he talked about the stack taking bath(shower) water and foul
water so I assumed that the next para. he meant 'grey water'.

If the two paras. are not directly related then fine - I understand what is
going on!

David W.E. Roberts wrote:
[Type your reply here]

The Natural Philosopher wrote:
David WE Roberts wrote:
"Nick Holmes" wrote in message
...
snip
Can this discharge be connected to an external cast iron soil pipe
(which in our 1906 build carries both bath(shower) outflow and foul
water from 2nd floor toilet (incidentally Cambridge's
edwardian/victorian houses have combined surface and foul water
connections to mains drainage which would not be permitted in a modern
property)).
snip

I am a bit puzzled by this - when I put a second bathroom in my 1930s
house around 2001/2 I had to run a new soil pipe to an existing manhole
and I fed both grey and black water into the same stack.

Building control were perfectly happy with this.

Is this a recent change, or does it not apply when working with older
properties?

Cheers

Dave R
More a function of your local water authority really.

But he was talking 'white' water, Rain collection.

All used water must be treated, black, brown or grey.

All rainwater ideally should end up in the subsoil or river system.

Still confused - he talked about the stack taking bath(shower) water and foul
water so I assumed that the next para. he meant 'grey water'.

If the two paras. are not directly related then fine - I understand what is
going on!



Sorry I have confused the issues. Probably it makes no difference where
you are, bath and toilet waste gets combined. In our case gutter flow
also gets run into the same waste pipe (though not the particular soil
stack I mentioned).

In answer to another post, we cant easily go to soakaway (property
boundary is 1m from cellar ext wall and external ground on our side is
concrete for 15m in both directions).

Locally, we have exemption for older properties with dual purpose
sewerage ('white' and grey/black).

best wishes

Nick
----------------------------
Nick Holmes

bof wrote:
In message , Nick Holmes
writes
bof wrote:
Re combi in the basement
I have one here, the condensate goes via gravity into a small tank
and is periodically pumped out by a small electric motor, the unit's
something like 8"x8"x4". The condesate is pumped through a narrow
bore, (about 1/2" ext dia) flexible tube under the floorboards and
out through the wall into an external drain. I was a bit dubious
before installation but it's been working well for the last two years.



Thanks for this. What about the pressure relief discharge pipe though?

There's a 15mm copper pipe goes out next to the flue, whether this is
for pressure relief or no I don't know



It sounds as though it might be - does how does the pipe terminate?

Doesn't the pressure relief discharge pipe have to be terminated so that
there is no risk of it spewing hot pressurised water onto anyone and
doesn't it need to run downwards from the pressure release valve (unless
through a trap and pump)?

--
best wishes

Nick
----------------------------
Nick Holmes

In message , Nick Holmes
writes
bof wrote:
In message , Nick Holmes
writes
bof wrote:
Re combi in the basement
I have one here, the condensate goes via gravity into a small tank
and is periodically pumped out by a small electric motor, the
unit's something like 8"x8"x4". The condesate is pumped through a
narrow bore, (about 1/2" ext dia) flexible tube under the
floorboards and out through the wall into an external drain. I was
a bit dubious before installation but it's been working well for




Thanks for this. What about the pressure relief discharge pipe though?
There's a 15mm copper pipe goes out next to the flue, whether this
is for pressure relief or no I don't know



It sounds as though it might be - does how does the pipe terminate?

Doesn't the pressure relief discharge pipe have to be terminated so
that there is no risk of it spewing hot pressurised water onto anyone
and doesn't it need to run downwards from the pressure release valve
(unless through a trap and pump)?

This runs down from the boiler then up 3' and out through the wall
terminating in an elbow about 6" above, and pointing at, the ground



--
bof at bof dot me dot uk

On Fri, 02 Oct 2009 13:00:21 +0100, Nick Holmes wrote:


However, I am struggling with the twin issues of condensate drain and
pressure relief discharge. If I understand correctly, the condensate
could be run into a syphonic trap with a pump to periodically discharge
it. Can this discharge be connected to an external cast iron soil pipe
(which in our 1906 build carries both bath(shower) outflow and foul
water from 2nd floor toilet (incidentally Cambridge's
edwardian/victorian houses have combined surface and foul water
connections to mains drainage which would not be permitted in a modern
property)).

As others have said this application calls for a condensate pump. You
shouldn't pipe acidic condensate into a metallic drain system. In the
case of cast-iron I suspect this is as much arse-covering in the event
that the CI finally rots through and the aggrieved owner scapegoats the
boiler installer, rather than a century's natural corrosion. If you are
both installer and owner you may decide not to worry, but you may
still find it hard to get your installer to commission such an
installation. A way around might be to use a condensate-neutralising
gadget (I think Salamander do one).



Also what about the requirement for the discharge pipe. Will this need
a different trap and pump and pipe - the type of possible flow being v
different?

That's more of a problem: it must not go uphill (otherwise when it does
discharge there's no way for the pipework to empty, and the water in it
will gradually dry out leaving dissolved salts behind, I guess - anyway
I'm pretty sure if you check your boiler manufacturer's instruction you'll
find it says no uphill runs). I suppose it could discharge via a tundish
into some sort of sump which is emptied via a sump pump, as for basements
prone to filling up with water, but I've never heard of such an
arrangement and it would be expensive. One way would be to fit a
heating-only boiler with a separate expansion vessel and PRD which could
be located higher up in the CH system where it could discharge downwards
and out. However that would rule out a combi (because in practice all
combis are system rather than heating-only types - have a look at the
article in the DIY FAQ wiki for an explanation of the different types).

In principle one could remove the PRD from a combi and run a pipe from its
connection point within the boiler to a point conveniently higher up and
re-fit the (or a) PRD there, but this would almost certainly not meet
with the manufacturers' approval (or that of the commissioning installer).

Might be worth talking to your boiler mfr about this - I'd have thought
the question must have arisen. If there's a satisfactory answer please let
us know back here!


--
John Stumbles -- http://yaph.co.uk

What is a simile like?

"YAPH" wrote in message
...
On Fri, 02 Oct 2009 13:00:21 +0100, Nick Holmes wrote:


Also what about the requirement for the discharge pipe. Will this need
a different trap and pump and pipe - the type of possible flow being v
different?

That's more of a problem: it must not go uphill (otherwise when it does
discharge there's no way for the pipework to empty, and the water in it
will gradually dry out leaving dissolved salts behind, I guess - anyway
I'm pretty sure if you check your boiler manufacturer's instruction you'll
find it says no uphill runs). I suppose it could discharge via a tundish
into some sort of sump which is emptied via a sump pump, as for basements
prone to filling up with water, but I've never heard of such an
arrangement and it would be expensive. One way would be to fit a
heating-only boiler with a separate expansion vessel and PRD which could
be located higher up in the CH system where it could discharge downwards
and out. However that would rule out a combi (because in practice all
combis are system rather than heating-only types - have a look at the
article in the DIY FAQ wiki for an explanation of the different types).

In principle one could remove the PRD from a combi and run a pipe from its
connection point within the boiler to a point conveniently higher up and
re-fit the (or a) PRD there, but this would almost certainly not meet
with the manufacturers' approval (or that of the commissioning installer).

Might be worth talking to your boiler mfr about this - I'd have thought
the question must have arisen. If there's a satisfactory answer please let
us know back here!


--
John Stumbles -- http://yaph.co.uk


What if you connect the boilers PRD into the CH flow or return and use a
seperate PRD higher up? I have seen it done but I do not know if it is
correct

Adam

In article ,
"ARWadsworth" writes:

"YAPH" wrote in message
...
On Fri, 02 Oct 2009 13:00:21 +0100, Nick Holmes wrote:


Also what about the requirement for the discharge pipe. Will this need
a different trap and pump and pipe - the type of possible flow being v
different?

That's more of a problem: it must not go uphill (otherwise when it does
discharge there's no way for the pipework to empty, and the water in it
will gradually dry out leaving dissolved salts behind, I guess - anyway
I'm pretty sure if you check your boiler manufacturer's instruction you'll
find it says no uphill runs). I suppose it could discharge via a tundish
into some sort of sump which is emptied via a sump pump, as for basements
prone to filling up with water, but I've never heard of such an
arrangement and it would be expensive. One way would be to fit a

Sounds like a way to get very badly burned, if you suddenly get 30+kW
worth of steam blasting into an inclosed space such as a cellar.

heating-only boiler with a separate expansion vessel and PRD which could
be located higher up in the CH system where it could discharge downwards
and out. However that would rule out a combi (because in practice all
combis are system rather than heating-only types - have a look at the
article in the DIY FAQ wiki for an explanation of the different types).

In principle one could remove the PRD from a combi and run a pipe from its
connection point within the boiler to a point conveniently higher up and
re-fit the (or a) PRD there, but this would almost certainly not meet
with the manufacturers' approval (or that of the commissioning installer).

Might be worth talking to your boiler mfr about this - I'd have thought
the question must have arisen. If there's a satisfactory answer please let
us know back here!

What if you connect the boilers PRD into the CH flow or return and use a
seperate PRD higher up? I have seen it done but I do not know if it is
correct

I don't recall anything which would have prevented doing this in
the installation instructions for my boiler (although I didn't
need to, and I haven't gone back to check them).

I think that to make this safe, I would say:

1 Pipework from boiler to PRV must be all metal (it's the route
which carries super-heated water and steam when boiler controls
fail, which is hotter than plastic pipe is designed for).

2 If the run is more than a couple of feet, increase to next pipe
size so as not to add undue flow restriction to the escape route.

3 No valves or isolation devices to be fitted between boiler and PRV.

Something I did as a result of previously observing the effects of
steam in pipework - make sure the pipe path from boiler to PRV and
to outside is clamped firmly enough to prevent soldered joins melted
by the steam from blowing the joins apart inside the house (again,
where the ejection of super-heated water and steam might cause injury).

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

On Mon, 05 Oct 2009 12:43:09 +0000, Andrew Gabriel wrote:

... I suppose it could discharge via a tundish
into some sort of sump which is emptied via a sump pump, as for basements
prone to filling up with water, but I've never heard of such an
arrangement and it would be expensive. One way would be to fit a

Sounds like a way to get very badly burned, if you suddenly get 30+kW
worth of steam blasting into an inclosed space such as a cellar.

You get tundish arrangements on unvented HW cylinders (ptui!) so that's
presumably OK. Or maybe not (ptui^2).



--
John Stumbles -- http://yaph.co.uk

An atheist is a person with no invisible means of support

"ARWadsworth" wrote in message
.com...

"YAPH" wrote in message
...
On Fri, 02 Oct 2009 13:00:21 +0100, Nick Holmes wrote:


Also what about the requirement for the discharge pipe. Will this need
a different trap and pump and pipe - the type of possible flow being v
different?

That's more of a problem: it must not go uphill (otherwise when it does
discharge there's no way for the pipework to empty, and the water in it
will gradually dry out leaving dissolved salts behind, I guess - anyway
I'm pretty sure if you check your boiler manufacturer's instruction
you'll
find it says no uphill runs). I suppose it could discharge via a tundish
into some sort of sump which is emptied via a sump pump, as for basements
prone to filling up with water, but I've never heard of such an
arrangement and it would be expensive. One way would be to fit a
heating-only boiler with a separate expansion vessel and PRD which could
be located higher up in the CH system where it could discharge downwards
and out. However that would rule out a combi (because in practice all
combis are system rather than heating-only types - have a look at the
article in the DIY FAQ wiki for an explanation of the different types).

In principle one could remove the PRD from a combi and run a pipe from
its
connection point within the boiler to a point conveniently higher up and
re-fit the (or a) PRD there, but this would almost certainly not meet
with the manufacturers' approval (or that of the commissioning
installer).

Might be worth talking to your boiler mfr about this - I'd have thought
the question must have arisen. If there's a satisfactory answer please
let
us know back here!


--
John Stumbles -- http://yaph.co.uk


What if you connect the boilers PRD into the CH flow or return and use a
seperate PRD higher up? I have seen it done but I do not know if it is
correct

I have seen this done. It is not the same as capping the Pressure Discharge
Valve and putting one elsewhere on the system. It relieves pressure at the
boiler to protects its components (where the [pressure builds up at the
burner) diverting the pressure to another point on the system where it can
be relieved to atmosphere.

"bof" wrote in message
...
In message , Nick Holmes
writes
bof wrote:
In message , Nick Holmes
writes
bof wrote:
Re combi in the basement
I have one here, the condensate goes via gravity into a small tank
and is periodically pumped out by a small electric motor, the unit's
something like 8"x8"x4". The condesate is pumped through a narrow
bore, (about 1/2" ext dia) flexible tube under the floorboards and
out through the wall into an external drain. I was a bit dubious
before installation but it's been working well for



Thanks for this. What about the pressure relief discharge pipe though?
There's a 15mm copper pipe goes out next to the flue, whether this is
for pressure relief or no I don't know



It sounds as though it might be - does how does the pipe terminate?

Doesn't the pressure relief discharge pipe have to be terminated so that
there is no risk of it spewing hot pressurised water onto anyone and
doesn't it need to run downwards from the pressure release valve (unless
through a trap and pump)?

This runs down from the boiler then up 3' and out through the wall
terminating in an elbow about 6" above, and pointing at, the ground

It is supposed to point back at the wall.

On Sat, 17 Oct 2009 02:09:27 +0100, Doctor Drivel wrote:

It is supposed to point back at the wall.

That's if it's way above ground: if it's close to the ground it can point
directly down. (Basically as long as when it blows it's not likely to blow
steam and scalding water directly over anyone.)


--
John Stumbles -- http://yaph.co.uk

The astronomer married a star