Hi. I've finally identified a strange copper pipe connection between the
flow from and return to my boiler as being a bypass circuit (with a gate
valve halfway along it).

From what I've read recently, bypass circuits are designed to protect
the pump in case the valve is open to the central heating circuit but
all the trvs have shut down. Looking at the four or five schematic
diagrams that I've seen, they all have the components in the following
order:

Flow from boiler
V
Pump
V
Bypass circuit (back to boiler)
V
Valve

This makes sense to me - if the valve has effectively closed, the pump
can still work by sending water around the bypass circuit back to the
boiler.

Here's my setup - it's an open vented fully pumped system with the
following bits:

Flow from boiler (Potterton Suprima 60L)
V
Bypass circuit (back to boiler)
V
Pump (Grundfos Selectric)
V
Valve (Sundial Y-plan V4073A1039)

Now, paraphrasing Snoop Doggy Dogg, "I ain't no plumber" - but this
looks wrong to me. If I close the valve down completely, the pump won't
be able to continue, because it's not included in the bypass circuit.

Only one question for the time being: is my deduction correct?

Jaime wrote:
Hi. I've finally identified a strange copper pipe connection between the
flow from and return to my boiler as being a bypass circuit (with a gate
valve halfway along it).
snip
Here's my setup - it's an open vented fully pumped system with the
following bits:

Flow from boiler (Potterton Suprima 60L)
V
Bypass circuit (back to boiler)
V
Pump (Grundfos Selectric)
V
Valve (Sundial Y-plan V4073A1039)

Now, paraphrasing Snoop Doggy Dogg, "I ain't no plumber" - but this
looks wrong to me. If I close the valve down completely, the pump won't
be able to continue, because it's not included in the bypass circuit.

Only one question for the time being: is my deduction correct?

I have not looked at the manual for the boiler.
Is it possible that it's a large circuit, and the external pump is
simply supplementary to the built in one?
In which case of course, there is no problem.

Ian Stirling wrote:
Jaime wrote:
Hi. I've finally identified a strange copper pipe connection between the
flow from and return to my boiler as being a bypass circuit (with a gate
valve halfway along it).
snip
Here's my setup - it's an open vented fully pumped system with the
following bits:

Flow from boiler (Potterton Suprima 60L)
V
Bypass circuit (back to boiler)
V
Pump (Grundfos Selectric)
V
Valve (Sundial Y-plan V4073A1039)

Now, paraphrasing Snoop Doggy Dogg, "I ain't no plumber" - but this
looks wrong to me. If I close the valve down completely, the pump won't
be able to continue, because it's not included in the bypass circuit.

Only one question for the time being: is my deduction correct?

I have not looked at the manual for the boiler.
Is it possible that it's a large circuit, and the external pump is
simply supplementary to the built in one?
In which case of course, there is no problem.

I've looked at the "Installation and Service Instructions" for the
Potterton Suprima 60L boiler and both of the schematic diagrams show the
external pump included in the bypass circuit (i.e. flow from boiler goes
to pump goes to bypass circuit goes to valve). Also, the boiler
documentation says nothing about a built-in pump...

On 2006-12-09 12:23:11 +0000, Jaime said:

Hi. I've finally identified a strange copper pipe connection between
the flow from and return to my boiler as being a bypass circuit (with a
gate valve halfway along it).

From what I've read recently, bypass circuits are designed to protect
the pump in case the valve is open to the central heating circuit but
all the trvs have shut down. Looking at the four or five schematic
diagrams that I've seen, they all have the components in the following
order:

Flow from boiler
V
Pump
V
Bypass circuit (back to boiler)
V
Valve

This makes sense to me - if the valve has effectively closed, the pump
can still work by sending water around the bypass circuit back to the
boiler.

Here's my setup - it's an open vented fully pumped system with the
following bits:

Flow from boiler (Potterton Suprima 60L)
V
Bypass circuit (back to boiler)
V
Pump (Grundfos Selectric)
V
Valve (Sundial Y-plan V4073A1039)

Now, paraphrasing Snoop Doggy Dogg, "I ain't no plumber" - but this
looks wrong to me. If I close the valve down completely, the pump won't
be able to continue, because it's not included in the bypass circuit.

Only one question for the time being: is my deduction correct?

Sounds like it, although the purpose is to keep a flow of water going
through the boiler to prevent so that when the valve closes, the water
doesn't become stationary and hence boil.

On Sat, 09 Dec 2006 14:12:29 +0000, Jaime wrote:

Ian Stirling wrote:
Jaime wrote:
Hi. I've finally identified a strange copper pipe connection between the
flow from and return to my boiler as being a bypass circuit (with a gate
valve halfway along it).
snip
Here's my setup - it's an open vented fully pumped system with the
following bits:

Flow from boiler (Potterton Suprima 60L)
V
Bypass circuit (back to boiler)
V
Pump (Grundfos Selectric)
V
Valve (Sundial Y-plan V4073A1039)

Now, paraphrasing Snoop Doggy Dogg, "I ain't no plumber" - but this
looks wrong to me. If I close the valve down completely, the pump won't
be able to continue, because it's not included in the bypass circuit.

Only one question for the time being: is my deduction correct?

I have not looked at the manual for the boiler.
Is it possible that it's a large circuit, and the external pump is
simply supplementary to the built in one?
In which case of course, there is no problem.

I've looked at the "Installation and Service Instructions" for the
Potterton Suprima 60L boiler and both of the schematic diagrams show the
external pump included in the bypass circuit (i.e. flow from boiler goes
to pump goes to bypass circuit goes to valve). Also, the boiler
documentation says nothing about a built-in pump...

Suprimas do not contains integral pumps the OP's set up is wrong. Depending
on the nature of the bypass ('smart' valve or 'dumb' gate valve) and the
nature of the rest of the heating circuit (S-plan, or Y-plan, TRVs
all/none/most) you may or may not get some over-run circulation as needed.


--
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
Gas Fitting Standards Docs he http://www.makewrite.demon.co.uk/GasFittingStandards