First, the problem.

The coldest room in the house is the lounge but the radiator without the
TRV is in the hall.

We don't always want to heat the lounge, but when we do we can overheat
the hall (and consequently the upstairs) especially if the wood burner in
the kitchen/dining/living area is chucking heat into the hall as well.

The thermostat is wireless so we can move it with us into the room we are
using at the time, and possibly shut off the other radiators.

So ideally we could do with a TRV in the hall.

However this would mean that all radiators have TRVs.

Now some Googling says this is O.K. and some says it is not.

I am thinking that if we have a twin pipe system (where there is a flow
and return pipe across which the radiators connect) or if we have a single
pipe system with the radiators all teed off for flow and return then there
should probably be enough water in the pipework to flow round and through
the boiler without overheating.

The house is a 1930s three bedroom semi.

So is it safe to TRV everything?

Or should I take a TRV off one of the bathroom radiators?

Cheers

Dave R

On 15/04/14 16:04, David.WE.Roberts wrote:
First, the problem.

The coldest room in the house is the lounge but the radiator without the
TRV is in the hall.

We don't always want to heat the lounge, but when we do we can overheat
the hall (and consequently the upstairs) especially if the wood burner in
the kitchen/dining/living area is chucking heat into the hall as well.

The thermostat is wireless so we can move it with us into the room we are
using at the time, and possibly shut off the other radiators.

So ideally we could do with a TRV in the hall.

However this would mean that all radiators have TRVs.

Now some Googling says this is O.K. and some says it is not.

I am thinking that if we have a twin pipe system (where there is a flow
and return pipe across which the radiators connect) or if we have a single
pipe system with the radiators all teed off for flow and return then there
should probably be enough water in the pipework to flow round and through
the boiler without overheating.

If you TRV everything you need either a limited short bypass - towel
rads are ideal for this, or a pressure based bypass valve. I think the
principle use is to stop the pump knackering itself with a totally "off"
hydraulic system.

On Tuesday, April 15, 2014 4:04:41 PM UTC+1, David.WE.Roberts wrote:

So is it safe to TRV everything?

Yes, if you do one of two things:
1) Install a bypass valve. This is a spring-loaded valve which allows water to flow when hte pressure exceeds a preset threshold. Otherwise when all the TRVs happen to shut off the back pressure will become very high which loads the pump more. Also, hte last valve to closed will make a lot of turbulence noise as it does so.

2) Install a new pump with electronic motor drive. These often have options to vary the pressure-flow curves in a helpful way. Some will just maintain constant pressure, while others will reduce the pressure as the flow drops. (I can't help feeling that there might be scope for instability in such a system, particularly if there are extra pumps for underfloor heating.)

John

On 2014-04-15, Tim Watts wrote:

On 15/04/14 16:04, David.WE.Roberts wrote:
....
However this would mean that all radiators have TRVs.

Now some Googling says this is O.K. and some says it is not.

I am thinking that if we have a twin pipe system (where there is a flow
and return pipe across which the radiators connect) or if we have a single
pipe system with the radiators all teed off for flow and return then there
should probably be enough water in the pipework to flow round and through
the boiler without overheating.

If you TRV everything you need either a limited short bypass - towel
rads are ideal for this, or a pressure based bypass valve. I think the
principle use is to stop the pump knackering itself with a totally "off"
hydraulic system.

Some combination boilers (& possibly other kinds, but I'm not sure)
now come with an internal bypass.

On Tue, 15 Apr 2014 08:17:26 -0700, jrwalliker wrote:

On Tuesday, April 15, 2014 4:04:41 PM UTC+1, David.WE.Roberts wrote:

So is it safe to TRV everything?

Yes, if you do one of two things:
1) Install a bypass valve. This is a spring-loaded valve which allows
water to flow when hte pressure exceeds a preset threshold. Otherwise
when all the TRVs happen to shut off the back pressure will become very
high which loads the pump more. Also, hte last valve to closed will
make a lot of turbulence noise as it does so.

2) Install a new pump with electronic motor drive. These often have
options to vary the pressure-flow curves in a helpful way. Some will
just maintain constant pressure, while others will reduce the pressure
as the flow drops. (I can't help feeling that there might be scope for
instability in such a system, particularly if there are extra pumps for
underfloor heating.)

John

Should have said that it is a combi so no chance of tinkering with the
pump.

Thanks to you and Tim - but I am still confused about the 'over pressure'.

I am assuming that there is a loop of pipe which can flow and return even
if all the radiators are turned off because otherwise if one TRV was shut
the whole system would stop.

In which case where does the bypass go?

Or is it that the pipe only loop is not enough volume?
I guess this may be the 'back pressure' bit although I am not clear how
the back pressure is eased by a radiator full of incompressible water
somewhere in the loop.

I've looked at an installation diagram for a bypass valve but that seems
to be on a gravity system where if both hot water and central heating
control valves are closed then the water has nowhere to go.

I am assuming that with a modern combi boiler this cannot happen.

Boiler is a Worcester Bosch CDi although can't find which power level at
the moment.

Cheers

Dave R

"Tim Watts" wrote in message
...
On 15/04/14 16:04, David.WE.Roberts wrote:
First, the problem.

The coldest room in the house is the lounge but the radiator without the
TRV is in the hall.

We don't always want to heat the lounge, but when we do we can overheat
the hall (and consequently the upstairs) especially if the wood burner in
the kitchen/dining/living area is chucking heat into the hall as well.

The thermostat is wireless so we can move it with us into the room we are
using at the time, and possibly shut off the other radiators.

So ideally we could do with a TRV in the hall.

However this would mean that all radiators have TRVs.

Now some Googling says this is O.K. and some says it is not.

I am thinking that if we have a twin pipe system (where there is a flow
and return pipe across which the radiators connect) or if we have a
single
pipe system with the radiators all teed off for flow and return then
there
should probably be enough water in the pipework to flow round and through
the boiler without overheating.

If you TRV everything you need either a limited short bypass - towel rads
are ideal for this, or a pressure based bypass valve. I think the
principle use is to stop the pump knackering itself with a totally "off"
hydraulic system.

All I do is fully open the TRVs where I need heat (and take the thermostat
there, obviously). The hall doesn't have a TRV but is shut completely off
anyway.



---
This email is free from viruses and malware because avast! Antivirus protection is active.
http://www.avast.com

In article ,
David.WE.Roberts wrote:
So is it safe to TRV everything?

Depends on the boiler installation - if it has a bypass loop. Probably not.

Or should I take a TRV off one of the bathroom radiators?

Normal is a towel rail in the bathroom. Which generally will never produce
too much heat to the room.

--
*If I agreed with you, we'd both be wrong.

Dave Plowman London SW
To e-mail, change noise into sound.

On 15/04/2014 16:42, David.WE.Roberts wrote:
On Tue, 15 Apr 2014 08:17:26 -0700, jrwalliker wrote:

On Tuesday, April 15, 2014 4:04:41 PM UTC+1, David.WE.Roberts wrote:

So is it safe to TRV everything?

Yes, if you do one of two things:
1) Install a bypass valve. This is a spring-loaded valve which allows
water to flow when hte pressure exceeds a preset threshold. Otherwise
when all the TRVs happen to shut off the back pressure will become very
high which loads the pump more. Also, hte last valve to closed will
make a lot of turbulence noise as it does so.

2) Install a new pump with electronic motor drive. These often have
options to vary the pressure-flow curves in a helpful way. Some will
just maintain constant pressure, while others will reduce the pressure
as the flow drops. (I can't help feeling that there might be scope for
instability in such a system, particularly if there are extra pumps for
underfloor heating.)

John

Should have said that it is a combi so no chance of tinkering with the
pump.

Thanks to you and Tim - but I am still confused about the 'over pressure'.

As the rad valves shut down and the flow deceases, the pressure
developed by the pump will increase. Automatic bypass valves use the
pressure increase to decide when to open.


I am assuming that there is a loop of pipe which can flow and return even
if all the radiators are turned off because otherwise if one TRV was shut
the whole system would stop.

No. Unless you have a bypass valve, the heating circuit will have flow
and return pipes which effectively go out to the furthest radiator. All
the other radiators are then teed off those. The system flow will only
stop if all the rad valves are closed.


In which case where does the bypass go?

On a combi it'd go from the flow to the return, just like a radiator.
Incidentally, it's not there to protect the pump. It's there to prevent
the boiler running with no flow, which could easily be curtains for it.


Or is it that the pipe only loop is not enough volume?
I guess this may be the 'back pressure' bit although I am not clear how
the back pressure is eased by a radiator full of incompressible water
somewhere in the loop.

There isn't a pipe-only loop, just the radiators. if at least one rad
valve is open, there will be some flow. Otherwise there won't.


I've looked at an installation diagram for a bypass valve but that seems
to be on a gravity system where if both hot water and central heating
control valves are closed then the water has nowhere to go.

I am assuming that with a modern combi boiler this cannot happen.

It can if the room stat calls for heat, all of the rads are shut-off and
there's no bypass valve.

Cheers,

Colin.

In message , David.WE.Roberts
writes
On Tue, 15 Apr 2014 08:17:26 -0700, jrwalliker wrote:

On Tuesday, April 15, 2014 4:04:41 PM UTC+1, David.WE.Roberts wrote:

So is it safe to TRV everything?

Yes, if you do one of two things:
1) Install a bypass valve. This is a spring-loaded valve which allows
water to flow when hte pressure exceeds a preset threshold. Otherwise
when all the TRVs happen to shut off the back pressure will become very
high which loads the pump more. Also, hte last valve to closed will
make a lot of turbulence noise as it does so.

2) Install a new pump with electronic motor drive. These often have
options to vary the pressure-flow curves in a helpful way. Some will
just maintain constant pressure, while others will reduce the pressure
as the flow drops. (I can't help feeling that there might be scope for
instability in such a system, particularly if there are extra pumps for
underfloor heating.)

John

Should have said that it is a combi so no chance of tinkering with the
pump.

Thanks to you and Tim - but I am still confused about the 'over pressure'.

I am assuming that there is a loop of pipe which can flow and return even
if all the radiators are turned off because otherwise if one TRV was shut
the whole system would stop.


Nope, there are flow and return pipes, rads are each fed off of these.
and the end of the pipes they will effectively be joined by a rad.

Closing down a TRV will only stop the flow through it's rad.

If you had a lop of pipe, water would go through there rather than
through the rads.

In which case where does the bypass go?




Typically between the CH feed and retrun pipes near the boiler
--
Chris French

On Tue, 15 Apr 2014 18:45:22 +0100, Colin Stamp wrote:

On 15/04/2014 16:42, David.WE.Roberts wrote:
On Tue, 15 Apr 2014 08:17:26 -0700, jrwalliker wrote:

On Tuesday, April 15, 2014 4:04:41 PM UTC+1, David.WE.Roberts wrote:

So is it safe to TRV everything?

Yes, if you do one of two things:
1) Install a bypass valve. This is a spring-loaded valve which allows
water to flow when hte pressure exceeds a preset threshold. Otherwise
when all the TRVs happen to shut off the back pressure will become
very high which loads the pump more. Also, hte last valve to closed
will make a lot of turbulence noise as it does so.

2) Install a new pump with electronic motor drive. These often have
options to vary the pressure-flow curves in a helpful way. Some will
just maintain constant pressure, while others will reduce the pressure
as the flow drops. (I can't help feeling that there might be scope for
instability in such a system, particularly if there are extra pumps
for underfloor heating.)

John

Should have said that it is a combi so no chance of tinkering with the
pump.

Thanks to you and Tim - but I am still confused about the 'over
pressure'.

As the rad valves shut down and the flow deceases, the pressure
developed by the pump will increase. Automatic bypass valves use the
pressure increase to decide when to open.


I am assuming that there is a loop of pipe which can flow and return
even if all the radiators are turned off because otherwise if one TRV
was shut the whole system would stop.

No. Unless you have a bypass valve, the heating circuit will have flow
and return pipes which effectively go out to the furthest radiator. All
the other radiators are then teed off those. The system flow will only
stop if all the rad valves are closed.

This is the bit which I am having trouble visualising.

Are you saying that in simple terms there are two pipes, one flow and one
return.
The two pipes are connected by the radiators (one side to the flow, the
other side to the return) so that if any radiator valve is open, water
will flow from the flow to the return.
However if all radiators are shut there is no direct connection between
the flow and return?

[Presumably this could be avoided if there was a bypass link at (or
beyond) the furthest radiator which wouldn't seem to add much load to the
system and would also ensure that hot water was always available to all
radiators instantly.]

Anyway, if this is the standard installation it looks as though I will
need a bypass valve, or one radiator with no TRV.

I'll probably swap TRVs between the hall and the lounge to get the non-TRV
radiator in the coldest part of the house.

snip


Cheers

Dave R

On Tue, 15 Apr 2014 15:04:41 +0000, David.WE.Roberts wrote:

First, the problem.

The coldest room in the house is the lounge but the radiator without the
TRV is in the hall.

We don't always want to heat the lounge, but when we do we can overheat
the hall (and consequently the upstairs) especially if the wood burner
in the kitchen/dining/living area is chucking heat into the hall as
well.

The thermostat is wireless so we can move it with us into the room we
are using at the time, and possibly shut off the other radiators.

So ideally we could do with a TRV in the hall.

However this would mean that all radiators have TRVs.

Now some Googling says this is O.K. and some says it is not.

I am thinking that if we have a twin pipe system (where there is a flow
and return pipe across which the radiators connect) or if we have a
single pipe system with the radiators all teed off for flow and return
then there should probably be enough water in the pipework to flow round
and through the boiler without overheating.

The house is a 1930s three bedroom semi.

So is it safe to TRV everything?

Or should I take a TRV off one of the bathroom radiators?

Gah!!

Slaps head

I have two plinth heaters in the kitchen/dining area.

These don't have TRVs (no point as they are buried underneath units) so
they are always flowing and returning.
The electric fans are controlled by a wall thermostat.
So I do have a flow and return loop through two radiators without TRVs.

So I can put a TRV in the hall.

Phew - that was harder than it should have been.

Cheers

Dave R