Hi,

I really need a new gas boiler and I just need to check something I've
been told.

One chap came round and quoted to replace the existing gravity system
with another gravity system (hot water is on gravity, radiators are
pumped). This is a conventional boiler.

Another chap came and said that it's against some regulations to fit
gravity systems and also wanted to sell me a combi for various reasons.
(easier to fit, more loft space, less corrosion due to sealed system and
might save me a few quid in gas bills)

Is it true that gravity systems are not allowed?

Also, the 2nd chap said he has to fit a room thermostat even though he
can't see the point in them as he fits those things on the radiators.
Is that right? You have to have a room thermostat now? The first guy
wasn't going to fit one.

Thanks.

Peter
--
http://www.beluga.freeserve.co.uk

Is it true that gravity systems are not allowed?

Basically, yes. Part L Approved Document states that you must make provision
to reduce primary circuit losses. The suggested method is to pump the
circuit (to make heat transfer quicker) and install a cylinder thermostat
(so the primary circuit is only heated when required). This keeps the
primary circuit cold, and the boiler off, most of the time, whilst still
keeping the cylinder at the correct temperature.

Also, the 2nd chap said he has to fit a room thermostat even though he
can't see the point in them as he fits those things on the radiators.
Is that right? You have to have a room thermostat now? The first guy
wasn't going to fit one.

You need to have a boiler interlock, which completely turns off the boiler's
burners when there is no call for heat. If you had TRVs on all radiators
(and a bypass, but no room stat), then when all the radiators turned off via
their TRVs, the boiler would still be pumping heated water round the bypass.
This is not good. It can be overcome either by installing a room thermostat
in a room without a TRV on the radiator, or by installing a flow switch on
the circuit (but after the bypass) so that the boiler knows when to stop.

Christian.

"Tony Bryer" wrote in message
...

Whether a combi is right for you or not depends on whether you bath or
shower and how many people in your family - the merits and demerits of
combi systems can be found in many past threads here.


Is it unrealistic to have a combi in a hard water area, unless you also have
a water softener installed?

James


---
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In an earlier contribution to this discussion,
Christian McArdle wrote:

Is it true that gravity systems are not allowed?

Basically, yes. Part L Approved Document states that you must make
provision to reduce primary circuit losses. The suggested method is
to pump the circuit (to make heat transfer quicker) and install a
cylinder thermostat (so the primary circuit is only heated when
required). This keeps the primary circuit cold, and the boiler off,
most of the time, whilst still keeping the cylinder at the correct
temperature.

You could achieve much of this with a C-Plan system, and *still* have a
gravity HW circuit - which I assume would meet the regs?

However, a fully pumped system would still be better - preferably an S-Plan
system.
--
Cheers,
Set Square
______
Please reply to newsgroup. Reply address is invalid.

In article , Peter
Smithson wrote:
One chap came round and quoted to replace the existing gravity system
with another gravity system (hot water is on gravity, radiators are
pumped). This is a conventional boiler.

This is not the way to go, regulations or no regulations. You need
either a fully pumped system or a combi and do need a thermostat
interlock as explained by Christian. You can realistically expect to see
your gas bills fall by 20-30% by spending an extra £200-300.

Whether a combi is right for you or not depends on whether you bath or
shower and how many people in your family - the merits and demerits of
combi systems can be found in many past threads here.

--
Tony Bryer SDA UK 'Software to build on' http://www.sda.co.uk
Free SEDBUK boiler database browser http://www.sda.co.uk/qsedbuk.htm

You could achieve much of this with a C-Plan system, and *still* have a
gravity HW circuit - which I assume would meet the regs?

Except that the poor gravity circulation might take ages to heat up the
cylinder. If you could prove that you had efficienct gravity circulation
that provided rapid Part L recovery, then it would be fine. This is rarely
achievable in practice, however.

Christian.

James wrote:
"Tony Bryer" wrote in message
...
=20
Whether a combi is right for you or not depends on whether you bath or
shower and how many people in your family - the merits and demerits of
combi systems can be found in many past threads here.

=20
=20
Is it unrealistic to have a combi in a hard water area, unless you also=
have
a water softener installed?

You only need a scale inhibitor, not a water softener. There are various =

types available: magnetic, electromagentic and phosphor-dosing. The=20
latter are cheapest but require replacement of the phosphor cartridge=20
approximately every year, at a cost of about =A315. They do however have =

the advantage over the other types that there is evidence that they do=20
actually work :-)

In article ,
says...

This is not the way to go, regulations or no regulations. You need
either a fully pumped system or a combi and do need a thermostat
interlock as explained by Christian. You can realistically expect to see
your gas bills fall by 20-30% by spending an extra £200-300.

Trouble is, he's quoting about £700 more than the other guy. I'm not
sure if this is down to him charging more or because he has to do a lot
more work. He'll be taking out the hot water cylinder and the loft
tanks and making all the pipework tidy. He sounded a lot more
interested in his work and I'd expect a more professional job. He's
also recommending an expensive boiler as he says they pay for
themseleves in terms of maintenence.


Whether a combi is right for you or not depends on whether you bath or
shower and how many people in your family - the merits and demerits of
combi systems can be found in many past threads here.

I've read some of those threads in the past. I think I'm an ideal combi
in that it's a small house with 2 people. The only thing against the
combi which is unusual to me is that our road often has power cuts due
to poor cableing in our street. The last one went on all day but I
could still have a shower and go out for the evening with my hot water
tank.

I think the combi is going to be better overall but money is tight. I
just wanted to check that the 2nd guy (expensive combi man) knew what he
was talking about and it sounds like he does.

Cheers

Peter


--
http://www.beluga.freeserve.co.uk

On Thu, 09 Sep 2004 13:01:29 +0100, James wrote:


"Tony Bryer" wrote in message
...

Whether a combi is right for you or not depends on whether you bath or
shower and how many people in your family - the merits and demerits of
combi systems can be found in many past threads here.


Is it unrealistic to have a combi in a hard water area, unless you also have
a water softener installed?


If you keep the temperature control down (people put it to maximum in the
vain hope of makeing the boiler produce a faster flow rate). Then the
scaling is not an issue. If the exchanger does become scaled then on many
modern combis you can fairly easily remove and descale the unit or replace
it. Phosphate dosing of the input water can also be used.

Some people believe in electromagnetically bewitching the water make sod
all diffeence AFAICT.

--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html

"Peter Smithson" wrote
| I've read some of those threads in the past. I think I'm an ideal
| combi in that it's a small house with 2 people. The only thing
| against the combi which is unusual to me is that our road often
| has power cuts due to poor cableing in our street. The last one
| went on all day but I could still have a shower and go out for
| the evening with my hot water tank.

If power is really that bad, then a small inverter will easily power the
combi (it only needs its electronics, gas valve and pump to be powered, same
as an ordinary boiler system) from a charged-up car battery.

Owain

"Christian McArdle" wrote in message .net...
Is it true that gravity systems are not allowed?

Basically, yes. Part L Approved Document states that you must make provision
to reduce primary circuit losses. The suggested method is to pump the
circuit (to make heat transfer quicker) and install a cylinder thermostat
(so the primary circuit is only heated when required). This keeps the
primary circuit cold, and the boiler off, most of the time, whilst still
keeping the cylinder at the correct temperature.

Also, the 2nd chap said he has to fit a room thermostat even though he
can't see the point in them as he fits those things on the radiators.
Is that right? You have to have a room thermostat now? The first guy
wasn't going to fit one.

You need to have a boiler interlock, which completely turns off the boiler's
burners when there is no call for heat. If you had TRVs on all radiators
(and a bypass, but no room stat), then when all the radiators turned off via
their TRVs, the boiler would still be pumping heated water round the bypass.
This is not good. It can be overcome either by installing a room thermostat
in a room without a TRV on the radiator, or by installing a flow switch on
the circuit (but after the bypass) so that the boiler knows when to stop.

Christian.

Surely the boiler senses the return water temp and turn itself off
when only the bypass is open? That's how our system works where all
rads have TRVs (including in the room with the thermostat) and the
bypass is a length of pipe in the airing cupboard with a gate valve.
It works fine and the boiler shuts down when all the TRVs close. Or is
that what you mean by a boiler interlock - just a temp sensor in the
boiler? Are they not standard?

MBQ

Surely the boiler senses the return water temp and turn itself off
when only the bypass is open? That's how our system works where all
rads have TRVs (including in the room with the thermostat) and the
bypass is a length of pipe in the airing cupboard with a gate valve.
It works fine and the boiler shuts down when all the TRVs close. Or is
that what you mean by a boiler interlock - just a temp sensor in the
boiler? Are they not standard?

The problem is that without a room thermostat or flow switch, the boiler
won't know when any TRVs are opened. What will actually happen is that the
boiler will start burning again once the circuit has cooled down a little.
Your system, if left on at the height of summer, would actually use gas.
This is not acceptable under the law.

Christian.

In an earlier contribution to this discussion,
MBQ wrote:


Surely the boiler senses the return water temp and turn itself off
when only the bypass is open? That's how our system works where all
rads have TRVs (including in the room with the thermostat) and the
bypass is a length of pipe in the airing cupboard with a gate valve.
It works fine and the boiler shuts down when all the TRVs close. Or is
that what you mean by a boiler interlock - just a temp sensor in the
boiler? Are they not standard?

MBQ

Not quite the same thing! The boiler certainly has a thermostat, and stops
firing when its temperature is reached. So the boiler will *initially* turn
itself off when all the TRVs close. BUT, the boiler will then cool down to
below its stat temperature - and will promptly fire again - even if there is
no demand from space or water heating. That's why a boiler interlock is
needed.
--
Cheers,
Set Square
______
Please reply to newsgroup. Reply address is invalid.

In article , Christian
McArdle wrote:

This is not good. It can be overcome either by installing a room
thermostat
in a room without a TRV on the radiator, or by installing a flow switch
on
the circuit (but after the bypass) so that the boiler knows when to
stop.

Is retrofitting a flow switch a practical option without modifying the
internal boiler wiring?

The house we're moving into needs to have the heating controls improved.
Currently there is no room stat and only the bedrooms have TRVs. The
"standard" approach of a room stat in the living room and TRVs
everywhere else doesn't appeal since there will be times when we will
want to heat parts of the house without heating the living room.
Separate zones would obviously be the best solution but I don't fancy
the task of ripping up floors and modifying the pipework layout to
achieve this.

The boiler has an integral bypass and (I think) claims to have anti
cycle logic so TRVs on all radiators would be the simplest approach. A
flow switch would undoubtedly improve efficiency but as far as I can see
the only extra electrical connections shown in the manual for the combi
boiler are for an external thermostat and for a frost stat. I imagine
the flow switch needs to cut out the burners but leave the pump running
so it can detect a TRV opening. I assume that connecting a flow switch
to the external thermostat terminals would just permanently shut down
the entire system when all the TRVs closed since it would turn off the
pump as well as the burners.

--
Mike Clarke

Is retrofitting a flow switch a practical option without modifying the
internal boiler wiring?

Correct. You may find it works with an additional external pump set to
minimum, if the boiler doesn't mind the extra help! The flow switch output
would connect to the thermostat input on the combi.

Whether this would work or not depends on the internal design on the combi.

Christian.

On Fri, 10 Sep 2004 09:45:58 +0100, "Christian McArdle"
wrote:

Surely the boiler senses the return water temp and turn itself off
when only the bypass is open? That's how our system works where all
rads have TRVs (including in the room with the thermostat) and the
bypass is a length of pipe in the airing cupboard with a gate valve.
It works fine and the boiler shuts down when all the TRVs close. Or is
that what you mean by a boiler interlock - just a temp sensor in the
boiler? Are they not standard?

The problem is that without a room thermostat or flow switch, the boiler
won't know when any TRVs are opened. What will actually happen is that the
boiler will start burning again once the circuit has cooled down a little.
Your system, if left on at the height of summer, would actually use gas.
This is not acceptable under the law.

Christian.


It can be done with an outside temperature sensor as well.....


..andy

To email, substitute .nospam with .gl

"Set Square" wrote in message ...
In an earlier contribution to this discussion,
MBQ wrote:


Surely the boiler senses the return water temp and turn itself off
when only the bypass is open? That's how our system works where all
rads have TRVs (including in the room with the thermostat) and the
bypass is a length of pipe in the airing cupboard with a gate valve.
It works fine and the boiler shuts down when all the TRVs close. Or is
that what you mean by a boiler interlock - just a temp sensor in the
boiler? Are they not standard?

MBQ

Not quite the same thing! The boiler certainly has a thermostat, and stops
firing when its temperature is reached. So the boiler will *initially* turn
itself off when all the TRVs close. BUT, the boiler will then cool down to
below its stat temperature - and will promptly fire again - even if there is
no demand from space or water heating. That's why a boiler interlock is
needed.

But this doesn't happen. I guess what must be happening is that the
room stat is shutting off the boiler before all the TRVs have closed.
Failing that, how do I tell if I have a boiler interlock or not?

MBQ

But this doesn't happen. I guess what must be happening is that the
room stat is shutting off the boiler before all the TRVs have closed.
Failing that, how do I tell if I have a boiler interlock or not?

If you have a room stat, then you almost certainly have a boiler interlock.

To test if you have a boiler interlock, with the system cold, set all TRVs
and room thermostats very low. Now turn the central heating on. If the
boiler fires, then you have no interlock.

Christian.