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Gravity CH, hot radiator prob. |
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| message from sPoNiX on 17 May 2004 |
Have a gravity central heating system. When ot water Only is selected
the first radiatior in the circuit gets hot. Obviously this is a
problem in the summer!
Would this likely be the non-return valve stuck open?
The valve is very difficult to get to as it's down behind the boiler.
I assume that the valve points downwards..is this correct?
Is there any problem in just leaving it as it is and turning off the
affected radiator during the summer?
sPoNiX
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| BigWallop replied to sPoNiX on 17 May 2004 |
It might be that this radiator is an open by-pass circuit in case of over
heating, so don't turn it off completely but close one the valves, anyone,
down a bit to see if it helps. If you open it fully then mark a spot on
the head gear that is inline with the pipe, then close it in and count how
many times the mark passes the pipe it will give you a rough idea of how
many turns it needs to make it close to half way open again.
{I know what mean} :-))
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| Set Square replied to BigWallop on 17 May 2004 |
But gravity systems don't normally have a by-pass - because they must have a
boiler which doesn't need pump over-run. In the summer, the pump is OFF -
and the HW is heated purely by gravity. The boiler has to be able to cope
with cycling on its own stat, with little or no flow, without over-heating!
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| Set Square replied to sPoNiX on 17 May 2004 |
Sounds like you've got gravity circulation round your CH circuit - but it's
only supposed to circulate when the pump is running.
The usual solution is to have a null-flow (rather than non-return) valve in
the CH circuit. This requires a positive pressure (as provided by the pump)
before it opens - and gravity alone isn't sufficient to open it.
Maybe this is what you've got, and maybe it's stuck open a bit. If only one
radiator is affected, it certainly won't hurt to turn it off. You just
*might* find that another one then gets hot instead.
It won't actually hurt if you turn them *all* off - as long as you remember
to turn them on again before trying to use the central heating.
You really need to fix it though - because otherwise you'll have radiators
getting hot when they don't need to (i.e. when the room stat has switched
the pump off) in the winter.
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| sPoNiX replied to Set Square on 17 May 2004 |
I assumed it was a one way valve as it has an arrow on it..so it's
likely to be a null-flow valve instead?
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| sPoNiX replied to Set Square on 17 May 2004 |
Thought: It could be a non-return valve though..? If it were poining
downwards, any hot water attempting to flow upwards (By convection)
would be stopped by the valve? When the pump cuts it it'd push water
the other way (ie against convection) the valve would open and the
radiators get hot.
sPoNiX
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| Set Square replied to sPoNiX on 17 May 2004 |
Thing is, though, that you can never be *sure* which way gravity circulation
will go. [In my previous house, the gravity flow between the boiler and hot
water cylinder occasionally went the wrong way - resulting in no water,
because I had a thermostatic valve in the "return" pipe!]
You must also have a return pipe - and if your flow decides to go *up* that,
a non-return valve won't stop it - but a valve requiring a bit of urge to
open it *will*.
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Archived message: Gravity CH, hot radiator prob. (UK D-I-Y Home Repairs)
