http://www.gasman.fsbusiness.co.uk/images/twopipe.jpg

My system is roughly as above (plus hot water tank and an extra radiator in the garage both with their own motorized valve, which are irrelevant to the question).

Whoever fitted the heating system put a pipe directly from flow to return (just to the right of the pump in the diagram above).

There's a gate valve on it with a red tap, which is switched off.

What is this for?

--
http://petersparrots.com
http://petersphotos.com

Light travels faster than sound. This is why some people
appear bright until you hear them speak.

In article op.wb3o4schytk5n5@i7-940,
"Lieutenant Scott" writes:
http://www.gasman.fsbusiness.co.uk/images/twopipe.jpg

My system is roughly as above (plus hot water tank and an extra radiator in the garage both with their own motorized valve, which are irrelevant to the question).

Whoever fitted the heating system put a pipe directly from flow to return (just to the right of the pump in the diagram above).

There's a gate valve on it with a red tap, which is switched off.

What is this for?

It's a crude bypass loop.
It ensures there's still a flow path even if all the radiators
shut off, and/or if the arrangement of valves for selecting
heating/hot water have a mode where they're all closed.

It probably shouldn't be shut off, unless the system has been
modified since the original installation and no longer needs
it. You can get special bypass loop valves to use instead of
the gate valve which only open when the pump is trying to push
against a closed circuit, so they don't bleed any flow into the
return when there's a real demand for heat.

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

On Sun, 01 Apr 2012 20:36:35 +0100, Andrew Gabriel wrote:

In article op.wb3o4schytk5n5@i7-940,
"Lieutenant Scott" writes:
http://www.gasman.fsbusiness.co.uk/images/twopipe.jpg

My system is roughly as above (plus hot water tank and an extra radiator in the garage both with their own motorized valve, which are irrelevant to the question).

Whoever fitted the heating system put a pipe directly from flow to return (just to the right of the pump in the diagram above).

There's a gate valve on it with a red tap, which is switched off.

What is this for?

It's a crude bypass loop.
It ensures there's still a flow path even if all the radiators
shut off, and/or if the arrangement of valves for selecting
heating/hot water have a mode where they're all closed.

It probably shouldn't be shut off, unless the system has been
modified since the original installation and no longer needs
it. You can get special bypass loop valves to use instead of
the gate valve which only open when the pump is trying to push
against a closed circuit, so they don't bleed any flow into the
return when there's a real demand for heat.

Ah I see, thanks.

It's possible I shut it off years ago and forgot.

It used to be on a timer, and only limited by the thermostatic valves on the radiators, so it could block the pump without it.

But I added a room stat and opened the radiator valves fully, so there will never be a blocked pump.

I'll leave it shut for maximum power output.

Would a pump actually break with no flow?

If so, what is the minimum flow required for the average pump? I could have the situation of only having one 10mm HEP pipe flowing (the garage circuit).

--
http://petersparrots.com
http://petersphotos.com

I'm not so think as you drunk I am...

In article op.wb3tdtbuytk5n5@i7-940,
"Lieutenant Scott" writes:
On Sun, 01 Apr 2012 20:36:35 +0100, Andrew Gabriel wrote:

In article op.wb3o4schytk5n5@i7-940,
"Lieutenant Scott" writes:
There's a gate valve on it with a red tap, which is switched off.

What is this for?

It's a crude bypass loop.
It ensures there's still a flow path even if all the radiators
shut off, and/or if the arrangement of valves for selecting
heating/hot water have a mode where they're all closed.

It probably shouldn't be shut off, unless the system has been
modified since the original installation and no longer needs
it. You can get special bypass loop valves to use instead of
the gate valve which only open when the pump is trying to push
against a closed circuit, so they don't bleed any flow into the
return when there's a real demand for heat.

Ah I see, thanks.

It's possible I shut it off years ago and forgot.

It used to be on a timer, and only limited by the thermostatic valves on the radiators, so it could block the pump without it.

But I added a room stat and opened the radiator valves fully, so there will never be a blocked pump.

Ideally, remove the TRV in the room with the stat, so it can't get
turned off. You fit a stop valve instead (no knobs to turn).

I'll leave it shut for maximum power output.

Would a pump actually break with no flow?

No, but the boiler's heat exchanger would - it would overheat.

If so, what is the minimum flow required for the average pump? I could have the situation of only having one 10mm HEP pipe flowing (the garage circuit).


You need to look at the boiler's instructions. The minimum is usually
given as the minimum length of pipework around the bypass loop, so it's
enough to absorb the heat still passing through the heat exchanger
after the burner switches off, without causing the overheat stat to
trip or the water in the exchanger to boil. Some modern boilers don't
need an external bypass loop.

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

On Sun, 01 Apr 2012 22:04:21 +0100, Andrew Gabriel wrote:

In article op.wb3tdtbuytk5n5@i7-940,
"Lieutenant Scott" writes:
On Sun, 01 Apr 2012 20:36:35 +0100, Andrew Gabriel wrote:

In article op.wb3o4schytk5n5@i7-940,
"Lieutenant Scott" writes:
There's a gate valve on it with a red tap, which is switched off.

What is this for?

It's a crude bypass loop.
It ensures there's still a flow path even if all the radiators
shut off, and/or if the arrangement of valves for selecting
heating/hot water have a mode where they're all closed.

It probably shouldn't be shut off, unless the system has been
modified since the original installation and no longer needs
it. You can get special bypass loop valves to use instead of
the gate valve which only open when the pump is trying to push
against a closed circuit, so they don't bleed any flow into the
return when there's a real demand for heat.

Ah I see, thanks.

It's possible I shut it off years ago and forgot.

It used to be on a timer, and only limited by the thermostatic valves on the radiators, so it could block the pump without it.

But I added a room stat and opened the radiator valves fully, so there will never be a blocked pump.

Ideally, remove the TRV in the room with the stat, so it can't get
turned off. You fit a stop valve instead (no knobs to turn).

I tend to leave all my doors open, so the whole house is at the same temperature.

I'd have to accidentally turn off six TRVs to cause a problem.

Mind you in the garage, only one (non thermostatic) valve. But its quite a number of turns, you couldn't knock it off by mistake.

I'll leave it shut for maximum power output.

Would a pump actually break with no flow?

No, but the boiler's heat exchanger would - it would overheat.

[ignore this line, I see you answered it below]
Surely the boiler would just cut out when it reached the desired water temperature and stay off, as it already does by cycling on and off to maintain the correct temperature in the flow pipe.

If so, what is the minimum flow required for the average pump? I could have the situation of only having one 10mm HEP pipe flowing (the garage circuit).

You need to look at the boiler's instructions. The minimum is usually
given as the minimum length of pipework around the bypass loop, so it's
enough to absorb the heat still passing through the heat exchanger
after the burner switches off, without causing the overheat stat to
trip or the water in the exchanger to boil. Some modern boilers don't
need an external bypass loop.

If it's just to remove that little bit of heat, I would imagine the flow through 10mm HEP would be sufficient.

Hang on a sec. If I switch off the heating at the point where the boiler is just about to stop burning, then no water is being pumped, and things don't break.

--
http://petersparrots.com
http://petersphotos.com

"You know that your landing gear is up and locked when it takes full power to taxi to the terminal."

In article op.wb3uophcytk5n5@i7-940,
"Lieutenant Scott" writes:
On Sun, 01 Apr 2012 22:04:21 +0100, Andrew Gabriel wrote:

In article op.wb3tdtbuytk5n5@i7-940,
"Lieutenant Scott" writes:

I tend to leave all my doors open, so the whole house is at the same temperature.

I'd have to accidentally turn off six TRVs to cause a problem.

One day, someone else might be living there.

Mind you in the garage, only one (non thermostatic) valve. But its quite a number of turns, you couldn't knock it off by mistake.

If so, what is the minimum flow required for the average pump? I could have the situation of only having one 10mm HEP pipe flowing (the garage circuit).

You need to look at the boiler's instructions. The minimum is usually
given as the minimum length of pipework around the bypass loop, so it's
enough to absorb the heat still passing through the heat exchanger
after the burner switches off, without causing the overheat stat to
trip or the water in the exchanger to boil. Some modern boilers don't
need an external bypass loop.

If it's just to remove that little bit of heat, I would imagine the flow through 10mm HEP would be sufficient.

Might be.

Hang on a sec. If I switch off the heating at the point where the boiler is just about to stop burning, then no water is being pumped, and things don't break.

The boiler probably has a run-on timer for the pump, to keep it
going for a minute or two after the call for heat input has gone
and burner has gone out.

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

On 01/04/2012 20:36, Andrew Gabriel wrote:
In articleop.wb3o4schytk5n5@i7-940,
"Lieutenant writes:
http://www.gasman.fsbusiness.co.uk/images/twopipe.jpg

My system is roughly as above (plus hot water tank and an extra radiator in the garage both with their own motorized valve, which are irrelevant to the question).

Whoever fitted the heating system put a pipe directly from flow to return (just to the right of the pump in the diagram above).

There's a gate valve on it with a red tap, which is switched off.

What is this for?

It's a crude bypass loop.
It ensures there's still a flow path even if all the radiators
shut off, and/or if the arrangement of valves for selecting
heating/hot water have a mode where they're all closed.

It probably shouldn't be shut off, unless the system has been
modified since the original installation and no longer needs
it. You can get special bypass loop valves to use instead of
the gate valve which only open when the pump is trying to push
against a closed circuit, so they don't bleed any flow into the
return when there's a real demand for heat.


Well, it would do if the gate valve was open a bit.
--
Cheers,
Roger
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