How can I tell if my existing gravity fed CH system has a radiator
bypass fitted?

I'm fitting TRVs and don't want to get into the situation where all
the TRVs shut but the pump is still trying to push water round the
radiators.

sponix

In an earlier contribution to this discussion,
s--p--o--n--i--x   wrote:


> How can I tell if my existing gravity fed CH system has a radiator
> bypass fitted?
>
> I'm fitting TRVs and don't want to get into the situation where all
> the TRVs shut but the pump is still trying to push water round the
> radiators.
>
> sponix


What do you mean by "gravity fed" - vented, as opposed to
sealed/pressurised - or do you mean that the hot water circuit uses
gravity/convection circulation rather than being pumped?

How many (if any) motorised valves are there - and are they 2-port or
3-port?

Does your system layout fit any of the 'Plans' in
http://content.honeywell.com/uk/homes/systems.htm ?

If so, which one?
-- 
Cheers,
Set Square
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On Mon, 19 Sep 2005 15:13:08 +0100, "Set Square" 
wrote:


>What do you mean by "gravity fed" - vented, as opposed to
>sealed/pressurised - or do you mean that the hot water circuit uses
>gravity/convection circulation rather than being pumped?

>How many (if any) motorised valves are there - and are they 2-port or
>3-port?


vented, no motorized valves


>Does your system layout fit any of the 'Plans' in
>http://content.honeywell.com/uk/homes/systems.htm ?

>If so, which one?


Probably the first one would be the closest...no zone valve though but
a non return valve instead.

sponix

In an earlier contribution to this discussion,
s--p--o--n--i--x   wrote:


> On Mon, 19 Sep 2005 15:13:08 +0100, "Set Square" 
> wrote:
>
>> What do you mean by "gravity fed" - vented, as opposed to
>> sealed/pressurised - or do you mean that the hot water circuit uses
>> gravity/convection circulation rather than being pumped?
>
>> How many (if any) motorised valves are there - and are they 2-port or
>> 3-port?
>
> vented, no motorized valves
>
>> Does your system layout fit any of the 'Plans' in
>> http://content.honeywell.com/uk/homes/systems.htm ?
>
>> If so, which one?
>
> Probably the first one would be the closest...no zone valve though but
> a non return valve instead.
>
> sponix


If you've got a gravity HW system and pumped CH system with no motorised
valves, you've pretty certainly haven't got a by-pass - and you don't need
one. A by-pass is only needed when the boiler needs to keep the pump running
for a bit after it has stopped firing, to stop it overheating - and the
water must have somewhere to go if all the zone valves are shut. Your boiler
is quite happy to heat just the HW, without the pump running at all, so it
obviously doesn't have this problem.

The pump needs to be controlled by a room thermostat located in a room whose
radiator *doesn't* have a TRV. The pumped water always has a path through
this radiator.You may need to throttle the lockshield valve a bit to make
sure that the room with the room stat doesn't get too hot too quickly and
shut the system down before the TRVs in the other rooms have had a chance to
do their thing.

While you are modifying the system, you really ought to convert it to at
least a C-Plan by fitting a 2-port zone valve and cylinder stat in the HW
circuit, and wiring it as per the Honeywell diagram. This will save a lot of
energy by shutting the boiler down when HW and CH demands are both
satisfied.
-- 
Cheers,
Set Square
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On Mon, 19 Sep 2005 18:48:40 +0100, "Set Square" 
wrote:


>If you've got a gravity HW system and pumped CH system with no motorised
>valves, you've pretty certainly haven't got a by-pass - and you don't need
>one. A by-pass is only needed when the boiler needs to keep the pump running
>for a bit after it has stopped firing, to stop it overheating - and the
>water must have somewhere to go if all the zone valves are shut. Your boiler
>is quite happy to heat just the HW, without the pump running at all, so it
>obviously doesn't have this problem.
>
>The pump needs to be controlled by a room thermostat located in a room whose
>radiator *doesn't* have a TRV. The pumped water always has a path through
>this radiator.You may need to throttle the lockshield valve a bit to make
>sure that the room with the room stat doesn't get too hot too quickly and
>shut the system down before the TRVs in the other rooms have had a chance to
>do their thing.


What I'm worried is someone will close fully the valve on the "bypass"
radiator, rather than use the room stat.

sponix

--s-p-o-n-i-x-- wrote:

> What I'm worried is someone will close fully the valve on the "bypass"
> radiator, rather than use the room stat.


Set it right, and put a lockshield on both ends.