Hi all

One of my colleagues is struggling with a combi system.

Problems a

Whistling boiler when CH or hot water calls for heat.
Total loss of pressure when boiler isn't running - returns to 1 bar when
boiler operational.

My knowledge of heating systems is limited to open-vented so any ideas
appreciated.


TIA

Phil

TheScullster wrote:
Hi all

One of my colleagues is struggling with a combi system.

Problems a

Whistling boiler when CH or hot water calls for heat.
Total loss of pressure when boiler isn't running - returns to 1 bar
when boiler operational.

Kettling perhaps? (Caused by system pressure being too low amongst other
things).

Tim

"Tim Downie" wrote in message
...
TheScullster wrote:
Hi all

One of my colleagues is struggling with a combi system.

Problems a

Whistling boiler when CH or hot water calls for heat.
Total loss of pressure when boiler isn't running - returns to 1 bar
when boiler operational.

Kettling perhaps? (Caused by system pressure being too low amongst other
things).

Tim




I would consider that it has no pressure - but when it gets hot it causes
some pressurisation.

Go to the good old FAQ and learn to bleed and pressurise the system.


John

"John" wrote

I would consider that it has no pressure - but when it gets hot it causes
some pressurisation.

Go to the good old FAQ and learn to bleed and pressurise the system.

I gave him a copy of the FAQ and he claims to have followed the procedure
for bleeding.
Not sure if he has added inhibitor though!
Would the lack of inhibitor allow sufficient build up of compressible gas to
lose the initial 1.5 Bar charge?

Phil

TheScullster wrote:

I gave him a copy of the FAQ and he claims to have followed the procedure
for bleeding.
Not sure if he has added inhibitor though!
Would the lack of inhibitor allow sufficient build up of compressible gas to
lose the initial 1.5 Bar charge?

Could be the classic failure of the expansion bottle problem. Boiler
runs, water expands, pressure rises above the pressure relief valve
limit and it blows off the excess pressure. When the system cools the
pressure in effect falls to zero. Bleeding all the rads would make this
worse rather than better.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
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| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

"John Rumm"wrote

Could be the classic failure of the expansion bottle problem. Boiler runs,
water expands, pressure rises above the pressure relief valve limit and it
blows off the excess pressure. When the system cools the pressure in
effect falls to zero. Bleeding all the rads would make this worse rather
than better.

John

Do I understand this right?
The diaphragm splits/holes, and when you bleed the system and fill it up
completely, you also fill the "air side" of the diaphragm in the expansion
vessel.
So when the boiler fires up, the pressure increases and relieves straight
away due to no expansion room.

How is it best to test this?
Pardon my ignorance, I have vented system myself.

Put a plastic bag over relief valve outlet?
Anything else like watching pressure?

Thanks

Phil

On Fri, 05 May 2006 09:13:43 +0100, TheScullster wrote:


"John Rumm"wrote

Could be the classic failure of the expansion bottle problem. Boiler runs,
water expands, pressure rises above the pressure relief valve limit and it
blows off the excess pressure. When the system cools the pressure in
effect falls to zero. Bleeding all the rads would make this worse rather
than better.

John

Do I understand this right?
The diaphragm splits/holes, and when you bleed the system and fill it up
completely, you also fill the "air side" of the diaphragm in the expansion
vessel.
So when the boiler fires up, the pressure increases and relieves straight
away due to no expansion room.

How is it best to test this?
Pardon my ignorance, I have vented system myself.

Put a plastic bag over relief valve outlet?
Anything else like watching pressure?

1) Put water in and bleed system of air to get a pressure of about 1.0 bar
cold.
2) Switch heating on and watch the pressure rise excessively and/or
throw water out the discharge pipe.
3) Observe pressure reduction to near zero after switching off heating.

Will need a new expansion vessel (repressuring may work but usually
doesn't fix it for more than a short while [1]) , maybe a new pressure
relief valve, maybe clearing out corrosion debris.

[1] Whatever caused the dry side pressure collapse will still exist.
--
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

TheScullster wrote:

Do I understand this right?
The diaphragm splits/holes, and when you bleed the system and fill it up
completely, you also fill the "air side" of the diaphragm in the expansion
vessel.
So when the boiler fires up, the pressure increases and relieves straight
away due to no expansion room.

Yup, spot on.

How is it best to test this?
Pardon my ignorance, I have vented system myself.

Put a plastic bag over relief valve outlet?

Yup.

Anything else like watching pressure?

Yup.

To fix it you have a few options:

You could try pumping up the pressure vessel (it will have a car tyre
like valve on it), however if it is knackered rather than just deflated
this won't help.

You could either replace it (can be tricky) or just add another one
somewhere else in the system.

If you need a quick fix bodge to keep things running you could half
empty a radiator so it has a big pocket of air in it. This will then act
as a pressure vessel for a bit.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/