We are in the process of having central heating installed, replacing an old
partial system. We have done this before in other properties so know
something about it. This property has 11 radiators. We are using a Honeywell
CM37z system with radio-linked TRVs on every radiator except for the
bathroom where the steam may corrode the electics of the radiator head.

Each radiator head in this system radios back to the relay unit that
controls the boiler. If any one radiator head calls for heat the boiler will
be active. If no radiator heads call for heat the boiler is off. There is no
separate room thermostat as this would be entirely without a purpose.

The CORGI registered man fitting the boiler for us is saying that we must
have a bypass. I know what this is. He says it is due to 'new' regulations.
He does not say whether these are building regulations or Corgi regulations.
He says "safety" and that he cannot sign it off (presumably Corgi-wise)
unless it has a bypass. He is saying that in theory if every radiator valve
failed and shut off, then the bypass radiator, which would be uncontrolled,
would allow the passage of water for safety reasons. He also says it will
save gas. The problem to us is he is insisting it must be one radiator that
remains uncontrolled. This is anathema to me! An uncontrolled radiator
chugging away every time the system is on for any one or more other
radiators.

Clearly this cannot save gas. I thought that a bypass was to protect the
circulating pump from pumping against nothing in the wildly unlikely event
that all TRVs were closed or faulty. Is there another function of a bypass?
Could we use a pipe or something automatic (I know there are various
so-called automatic bypasses) instead, rather than a radiator? As we do not
have a radiator in a room with a system thermostat. Our system will only
fire the boiler if one or more stats calls for heat. I take this to mean it
is fully interlocked?

Does any regulatory body, e.g. Building Regs or CORGI specify a bypass as
mandatory? If they ever do, does a system that would not call for heat in
the situation where all TRVs are -shut- require a bypass? Is it true to say
the bypass is a safety item or is it to protect the pump? Or in some way
supposed to save energy?

What should I read? Has anyone any references? Any input would be most
appreciated

Nick

"t" wrote in message
...

The CORGI registered man fitting the boiler for us is saying that we must
have a bypass. I know what this is. He says it is due to 'new'
regulations. He does not say whether these are building regulations or
Corgi regulations.

None. Corgi is a registration authority only. You indicate that the
bathroom rad has no thermostat valve on it. If so the by-pass is there. If
it does, say a mechanical one, then a mechanical by-pass between the flow
and return at the boiler may be fitted.

If you have electric thermostat valves on all rads then no by-pass is needed
if the boiler is control "interlocked". That is when all are off the pump
and boiler is off. You may want to put a by-pass in to maintain a minimum
flow through the boiler if only one rad is partially open.

Another way is to have a Grundfoss Alpha auto speed pump and a flow switch
on the reads return. When all rads are closed the flow switch cuts out the
boiler but not pump. No flow and the pumps automatically winds down. when
one opens it winds back up.

He says "safety" and that he cannot
sign it off (presumably Corgi-wise) unless it has a bypass. He is saying
that in theory if every radiator valve failed and shut off, then the
bypass radiator, which would be uncontrolled, would allow the passage of
water for safety reasons. He also says it will save gas. The problem to us
is he is insisting it must be one radiator that remains uncontrolled. This
is anathema to me! An uncontrolled radiator chugging away every time the
system is on for any one or more other radiators.

He is talking balls. The Baxi 133 HE Plus and Potterton Promax have an
integral flow switch and rad valves can be fitted on all rads. What if that
flow switch fails?

Clearly this cannot save gas. I thought that a bypass was to protect the
circulating pump from pumping against nothing in the wildly unlikely event
that all TRVs were closed or faulty.

A Grundfoss Alpha solves that.

Flow switches:
A selection at Hawco http://www.hawco.co.uk, but have a £75 min order. Try
RS: http://www.rswww.com
Farnell http://www.farnell.co.uk)
Also: http://www.axdistribution.com/FluidM...ow_switchs.htm

Flow switches from Farnell:
FS-05 (3A contacts) 3/4" BSP - £16
FS-01 (3A contacts) 22mm compression £31.92. Twice the price for
compression joints.

Data sheets:
http://www.farnell.com/datasheets/28551.pdf

Is there another function of a bypass?

It is there to maintain the minimum flow through the boiler. Some flow
switches have a minimum flow switch-on. Find out min' boiler flow and match
switch to suit. Fit an Alpha pump. If the flow switch is too low a flow
rate for the boiler, then have a tee before and after the flow switch and
by-pass the switch with 15mm pipe, in this pipe have an in-line isolator
valve. This then will raise the minimum flow through the boiler before
switching in the burner. A fix speed pump can be used as it will pump
around the flow switch by-pass, only when flow get to the min boiler level
will the flow switch, switch in and the burner come in.

Could we use a pipe or something automatic (I know there are various
so-called automatic bypasses) instead, rather than a radiator? As we do
not have a radiator in a room with a system thermostat. Our system will
only fire the boiler if one or more stats calls for heat. I take this to
mean it is fully interlocked?

The problem is the minimum flow through the boiler. If one rad is calling
and just about open it may not be enough flow. The flow switch combined
with a Grundfoss Alpha pump will maintain the min flow

Does any regulatory body, e.g. Building Regs or CORGI specify a bypass as
mandatory?

No. Just a control interlcok, which you have, and makers specs of course.

If they ever do, does a system that would not call for heat in the
situation where all TRVs are -shut- require a bypass?

The minimum flow problem again. You could have one thermo rad valve
permanently partially open, to give the min flow if another rad is open. Do
the rad valves have a min/max switching adjustment? If so you are sorted,
and no Alpha pump needed.

Is it true to say the bypass is a safety item or is it to protect the
pump? Or in some way supposed to save energy?

What should I read? Has anyone any references? Any input would be most
appreciated

Just ask me questions.

On Fri, 31 Mar 2006 23:45:07 +0100, t wrote:

We are in the process of having central heating installed, replacing an old
partial system. We have done this before in other properties so know
something about it. This property has 11 radiators. We are using a Honeywell
CM37z system with radio-linked TRVs on every radiator except for the
bathroom where the steam may corrode the electics of the radiator head.

Each radiator head in this system radios back to the relay unit that
controls the boiler. If any one radiator head calls for heat the boiler will
be active. If no radiator heads call for heat the boiler is off. There is no
separate room thermostat as this would be entirely without a purpose.

The CORGI registered man fitting the boiler for us is saying that we must
have a bypass. I know what this is. He says it is due to 'new' regulations.
He does not say whether these are building regulations or Corgi regulations.
He says "safety" and that he cannot sign it off (presumably Corgi-wise)
unless it has a bypass. He is saying that in theory if every radiator valve
failed and shut off, then the bypass radiator, which would be uncontrolled,
would allow the passage of water for safety reasons. He also says it will
save gas. The problem to us is he is insisting it must be one radiator that
remains uncontrolled. This is anathema to me! An uncontrolled radiator
chugging away every time the system is on for any one or more other
radiators.

Clearly this cannot save gas. I thought that a bypass was to protect the
circulating pump from pumping against nothing in the wildly unlikely event
that all TRVs were closed or faulty. Is there another function of a bypass?
Could we use a pipe or something automatic (I know there are various
so-called automatic bypasses) instead, rather than a radiator? As we do not
have a radiator in a room with a system thermostat. Our system will only
fire the boiler if one or more stats calls for heat. I take this to mean it
is fully interlocked?

Does any regulatory body, e.g. Building Regs or CORGI specify a bypass as
mandatory? If they ever do, does a system that would not call for heat in
the situation where all TRVs are -shut- require a bypass? Is it true to say
the bypass is a safety item or is it to protect the pump? Or in some way
supposed to save energy?

What should I read? Has anyone any references? Any input would be most
appreciated

There are two things he
1) Do you need a bypass. Yes.
2) Do you need one rad without a TRV. Not in this case.

Essentially you have a very extended S-plan system with each radiator
effective become a zone. Any one radiator will make for a boiler demand
(although in practice the likelihood is that several will be near calling
for heat if they are not already doing so).

Since the closing of all TRVs shuts off the boiler there IS an interlock
between the house being warm enough and the boiler demand.
So in this case the usual advice that you need a wall thermostat and a
nearby radiator without a TRV can be specifically ignored.

The bypass is almost certainly needed to provide a path for primary water
to continue after the demand has ceased. The boiler will need this (some
have this device internally so no need to add an extra one on the pipework).

The valve must be 'smart' not simply a gate valve on a piece of pipe with
the handle removed. Using a radiator (often the bathroom towel rail)
for a bypass is also no longer acceptable.

This is to comply with Part-L. CORGI are involved with this is as much as
if the fitter is discovered to have been self-certifying non-compliant
installations then he will put his registration in jeopardy. CORGI have an
inspection process - he may get caught out.

HTH


--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://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
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html

"Ed Sirett" wrote in message
news
On Fri, 31 Mar 2006 23:45:07 +0100, t wrote:

We are in the process of having central heating installed, replacing an
old
partial system. We have done this before in other properties so know
something about it. This property has 11 radiators. We are using a
Honeywell
CM37z system with radio-linked TRVs on every radiator except for the
bathroom where the steam may corrode the electics of the radiator head.

Each radiator head in this system radios back to the relay unit that
controls the boiler. If any one radiator head calls for heat the boiler
will
be active. If no radiator heads call for heat the boiler is off. There is
no
separate room thermostat as this would be entirely without a purpose.

The CORGI registered man fitting the boiler for us is saying that we must
have a bypass. I know what this is. He says it is due to 'new'
regulations.
He does not say whether these are building regulations or Corgi
regulations.
He says "safety" and that he cannot sign it off (presumably Corgi-wise)
unless it has a bypass. He is saying that in theory if every radiator
valve
failed and shut off, then the bypass radiator, which would be
uncontrolled,
would allow the passage of water for safety reasons. He also says it will
save gas. The problem to us is he is insisting it must be one radiator
that
remains uncontrolled. This is anathema to me! An uncontrolled radiator
chugging away every time the system is on for any one or more other
radiators.

Clearly this cannot save gas. I thought that a bypass was to protect the
circulating pump from pumping against nothing in the wildly unlikely
event
that all TRVs were closed or faulty. Is there another function of a
bypass?
Could we use a pipe or something automatic (I know there are various
so-called automatic bypasses) instead, rather than a radiator? As we do
not
have a radiator in a room with a system thermostat. Our system will only
fire the boiler if one or more stats calls for heat. I take this to mean
it
is fully interlocked?

Does any regulatory body, e.g. Building Regs or CORGI specify a bypass as
mandatory? If they ever do, does a system that would not call for heat in
the situation where all TRVs are -shut- require a bypass? Is it true to
say
the bypass is a safety item or is it to protect the pump? Or in some way
supposed to save energy?

What should I read? Has anyone any references? Any input would be most
appreciated

There are two things he
1) Do you need a bypass. Yes.

Open to question. It is NOT a definite yes at all.

2) Do you need one rad without a TRV. Not in this case.

Essentially you have a very extended S-plan system with each radiator
effective become a zone. Any one radiator will make for a boiler demand
(although in practice the likelihood is that several will be near calling
for heat if they are not already doing so).

Since the closing of all TRVs shuts off the boiler there IS an interlock
between the house being warm enough and the boiler demand.
So in this case the usual advice that you need a wall thermostat and a
nearby radiator without a TRV can be specifically ignored.

The bypass is almost certainly
needed to provide a path for primary water
to continue after the demand has ceased.

depends on what the boiler manufacturers say.

The boiler will need this (some
have this device internally so
no need to add an extra one
on the pipework).

Open to question.

The valve must be 'smart' not
simply a gate valve on a piece of pipe with
the handle removed. Using a radiator
(often the bathroom towel rail)
for a bypass is also no longer acceptable.

It is. The idea is to:

1. Provide a minimum flow through the boiler.
2. Pump overrun to dissipate heat from the boiler.

A bathroom rad could do this. An auto by-pass valve is not desirable. as it
raises the return temperature lowering efficiency. A flow switch, switching
the burner, with a parallel by-pass is probably the answer.

This is to comply with Part-L. CORGI
are involved with this is as much as
if the fitter is discovered to have been
self-certifying non-compliant
installations then he will put his
registration in jeopardy. CORGI have an
inspection process - he may get caught out.

A pity the CORGI man doesn't know that much. All too typical. They arm
wave a lot.

On Sat, 01 Apr 2006 15:51:28 +0100, in uk.d-i-y Ed Sirett
wrote:

If I can elaborate on Ed's advice ...

On Fri, 31 Mar 2006 23:45:07 +0100, t wrote:

We are in the process of having central heating installed, replacing an old
partial system. We have done this before in other properties so know
something about it. This property has 11 radiators. We are using a Honeywell
CM37z system with radio-linked TRVs on every radiator except for the
bathroom where the steam may corrode the electics of the radiator head.

Under the new Building Regs, Part L, this is no longer sufficient. You
must have a separate timer for the hot water (perhaps you have done
this) if the whole system is being replaced.

See "Heating controls" in
http://portal.est.org.uk/uploads/doc...dings/ce53.pdf

What should I read? Has anyone any references? Any input would be most
appreciated

The Honeywell guide summarises things reasonably well
http://content.honeywell.com/uk/homes/Regulations.htm

[snip]

The bypass is almost certainly needed to provide a path for primary water
to continue after the demand has ceased. The boiler will need this (some
have this device internally so no need to add an extra one on the pipework).

Indeed. For example, from my daughter's Ariston EuroCombi A/23 - A/27
MFFI Installation Manual ....

"By-pass: The appliance includes an automatic by-pass valve, which
protects the main heat exchanger in case of reduced or interrupted water
circulation through the heating system, due to the closing of
thermostatic valves or cock-type valves within the system."

This requirement to have a by-pass valve (not necessarily automatic)
stems from the boiler manufacturers installation requirements rather
than from 'regulations'. However, the new "Basic and Best Practice
Specifications" calls for an automatic valve to be used, rather than the
old way of a fixed gate valve.

Central Heating System Specifications (CHeSS) - Year 2005
http://www.est.org.uk/download.cfm?p=1&pid=544

"An automatic bypass valve controls water flow in accordance with
the water pressure across it, and is used to maintain a minimum flow
rate through the boiler and to limit circulation pressure when
alternative water paths are closed. A bypass circuit must be installed
if the boiler manufacturer requires one, or specifies that a minimum
flow rate has to be maintained while the boiler is firing.The installed
bypass circuit must then include an automatic bypass valve (not a
fixed-position valve). Care must be taken to set up the automatic bypass
valve correctly, so as to achieve the minimum flow rate required (but
not more) when alternative water paths are closed."

The valve must be 'smart' not simply a gate valve on a piece of pipe with
the handle removed.

Only needs to be smart in the sense that it opens according to the water
pressure across it - doesn't need any fancy electronics. e.g.
http://www.danfoss-randall.co.uk/def...lt=tem1019.asp


Phil
The uk.d-i-y FAQ is at http://www.diyfaq.org.uk/
The Google uk.d-i-y archive is at http://tinyurl.com/65kwq
Remove NOSPAM from address to email me

On Sun, 02 Apr 2006 19:16:32 +0000, Phil Addison wrote:

On Sat, 01 Apr 2006 15:51:28 +0100, in uk.d-i-y Ed Sirett
wrote:

If I can elaborate on Ed's advice ...

On Fri, 31 Mar 2006 23:45:07 +0100, t wrote:

We are in the process of having central heating installed, replacing an old
partial system. We have done this before in other properties so know
something about it. This property has 11 radiators. We are using a Honeywell
CM37z system with radio-linked TRVs on every radiator except for the
bathroom where the steam may corrode the electics of the radiator head.

Under the new Building Regs, Part L, this is no longer sufficient. You
must have a separate timer for the hot water (perhaps you have done
this) if the whole system is being replaced.

I had assumed that there would a master time clock for the heating.



The valve must be 'smart' not simply a gate valve on a piece of pipe with
the handle removed.

Only needs to be smart in the sense that it opens according to the water
pressure across it - doesn't need any fancy electronics. e.g.

Yes, by smart I simply meant that it must be sensitive to the differential
flow-return pressure,not just a semi-open valve.
The latter has the double disadvantage that it
i) Effectively reduces the boiler output thus requiring a bigger unit
than needed to be installed.
ii) Raises the temperature of the return water at all times thus reducing
the boiler efficiency.


--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://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
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html

"Phil Addison" wrote in message
...
On Sat, 01 Apr 2006 15:51:28 +0100, in uk.d-i-y Ed Sirett
wrote:

If I can elaborate on Ed's advice ...

On Fri, 31 Mar 2006 23:45:07 +0100, t wrote:

We are in the process of having central heating installed, replacing an
old
partial system. We have done this before in other properties so know
something about it. This property has 11 radiators. We are using a
Honeywell
CM37z system with radio-linked TRVs on every radiator except for the
bathroom where the steam may corrode the electics of the radiator head.

Under the new Building Regs, Part L, this is no longer sufficient. You
must have a separate timer for the hot water (perhaps you have done
this) if the whole system is being replaced.

See "Heating controls" in
http://portal.est.org.uk/uploads/doc...dings/ce53.pdf

What should I read? Has anyone any references? Any input would be most
appreciated

The Honeywell guide summarises things reasonably well
http://content.honeywell.com/uk/homes/Regulations.htm

[snip]

The bypass is almost certainly needed to provide a path for primary water
to continue after the demand has ceased. The boiler will need this (some
have this device internally so no need to add an extra one on the
pipework).

Indeed. For example, from my daughter's Ariston EuroCombi A/23 - A/27
MFFI Installation Manual ....

"By-pass: The appliance includes an automatic by-pass valve, which
protects the main heat exchanger in case of reduced or interrupted water
circulation through the heating system, due to the closing of
thermostatic valves or cock-type valves within the system."

This requirement to have a by-pass valve (not necessarily automatic)
stems from the boiler manufacturers installation requirements rather
than from 'regulations'. However, the new "Basic and Best Practice
Specifications" calls for an automatic valve to be used, rather than the
old way of a fixed gate valve.

Best practice is a "recommendation" only. There are better ways of doing it
rather than with a auto by-pass valve. An auto by-pass valve lowers the
efficiency of condensing boilers.

Central Heating System Specifications (CHeSS) - Year 2005
http://www.est.org.uk/download.cfm?p=1&pid=544

"An automatic bypass valve controls water flow in accordance with
the water pressure across it, and is used to maintain a minimum flow
rate through the boiler and to limit circulation pressure when
alternative water paths are closed. A bypass circuit must be installed
if the boiler manufacturer requires one, or specifies that a minimum
flow rate has to be maintained while the boiler is firing.The installed
bypass circuit must then include an automatic bypass valve (not a
fixed-position valve). Care must be taken to set up the automatic bypass
valve correctly, so as to achieve the minimum flow rate required (but
not more) when alternative water paths are closed."

That explains what a by-pass does. It does not say you "have" to have one.
Read my post on this.

Bypasses, Room thermostat or flow switches all of interest as I am
sorting out the spec for my replacement system.

The TRVs + flowswitch plus Grundfoss Alpha does seem the logical
approach - I hate the single room thermostat approach and find that in
the type of houses I have had they are useless at providing sensible
control of when the boiler is required to be providing heat.

but re Grundfoss Alpha pump and bypass

Can the pump in condensing combi boilers such as the Worcester and
Valliant range be replaced with a Grundfoss Alpha or are you stuck
with the "manufacturers" specified type ?

Robert

On Sun, 02 Apr 2006 22:28:18 +0100, in uk.d-i-y Ed Sirett
wrote:

On Sun, 02 Apr 2006 19:16:32 +0000, Phil Addison wrote:

On Sat, 01 Apr 2006 15:51:28 +0100, in uk.d-i-y Ed Sirett
wrote:

If I can elaborate on Ed's advice ...

On Fri, 31 Mar 2006 23:45:07 +0100, t wrote:

We are in the process of having central heating installed, replacing an old
partial system. We have done this before in other properties so know
something about it. This property has 11 radiators. We are using a Honeywell
CM37z system with radio-linked TRVs on every radiator except for the
bathroom where the steam may corrode the electics of the radiator head.

Under the new Building Regs, Part L, this is no longer sufficient. You
must have a separate timer for the hot water (perhaps you have done
this) if the whole system is being replaced.

I had assumed that there would a master time clock for the heating.

No criticism of you Ed. I was just adding some info for the general
readership.

Phil
The uk.d-i-y FAQ is at http://www.diyfaq.org.uk/
The Google uk.d-i-y archive is at http://tinyurl.com/65kwq
Remove NOSPAM from address to email me

robert wrote in message ...
Bypasses, Room thermostat or flow switches all of interest as I am
sorting out the spec for my replacement system.

The TRVs + flowswitch plus Grundfoss Alpha does seem the logical
approach - I hate the single room thermostat approach and find that in
the type of houses I have had they are useless at providing sensible
control of when the boiler is required to be providing heat.

but re Grundfoss Alpha pump and bypass

Can the pump in condensing combi boilers such as the Worcester and
Valliant range be replaced with a Grundfoss Alpha or are you stuck
with the "manufacturers" specified type ?

Some makers say you can fit them as a direct replacement. Others say no, as
they don't want any deviation from the norm. In most cases you can replace
like for like if it fits in. There is a larger control box on the Alpha.

Using an Alpha with an auto by-pass sometimes may not open the auto by-pass.
See this page of auto by-pass setup:
http://www.grundfos.co.uk/web/homeuk.nsf/vDocumentsDescending/8DBC6A2C79D5E6EF80256F7B00321AD3?OpenDocument

A flow switch with a settable by-pass around it is the best option when
using an Alpha pump. Or if you can get a flow switch which switches off the
burner when flow is below the minimum the boilers makers stipulate.

"Christian McArdle" wrote in message
...
The CORGI registered man fitting the boiler for us is saying that we must
have a bypass.

Only the boiler manufacturer can
specify if the boiler needs a bypass.

The makers specify a minimum flow. How you do that is your business. An
auto by-pass is only one way, but can be problematic it fails and lowers
efficiency raising the return temperature. Most fitted, like 90% of them,
are incorrectly set anyway. Best avoided.