slight leak in central heating

i have a worcester-bosch condensing boiler.
there is a slight leak, which i have not been able to track down, so was considering adding an internal leak sealer (fernox or similar)
The boiler manual states the use of such sealants is not recommended as it could lead to deposits in the heat exchanger.
Is this a real danger, and if so what are the likely side effects? ( reduced efficiency, need to replace the heat exchanger, etc,etc).
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All of the above. If they say don't, they do mean it.
Have a look carefully at all the radiator valves, both ends.
A favourite leak condition is that there is a small seep while hot but which is hardly noticed and maybe evaporates with the heat.
Otherwise more detective work is needed.
What's the rate of pressure drop?

.andy
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One appeared in my system a week ago. Couldn't find it anywhere. Left system off/cold for a while, and it was then quite obvious (leaking blanking plug at top of radiator). With system on, no moisture appears as it instantly dries.
--
Andrew Gabriel

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thanks for replies.
I noticed one of the radiators was not getting hot at the top, and the pressure gauge was above its normal level, so bled the air from the radiator.
This gave approx 1/2 bar pressure drop, needing a small amount of topping up.
I had to do the same thing once last winter (bleeding the same rad). Is this significant? Could the problem be close to this rad?
I check the pressure once a week so the problem seems to occur quickly, but then the system will operate for ages without a problem.
Over the summer, there didnt appear to be any loss of pressure when the heating was off for ages.
I did check under the upstairs floorboards when I was decorating/putting down carpet recently, but didnt see any obvious signs of leaking on the boards/plasterboard.
I'll check the valves carefully.
Could it be when the heating season starts, all the rads in the house are turned up. If there is a dodgy valve, it might start leaking then??????
wrote:

it
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I could be. Take the caps off and look for stain deposits.
Another possibility if you don't have inhibitor or if more is needed is that you have hydrogen being generated in the radiators.
.andy
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Is there an easy test for hydrogen?
(get out a match, and stand well back.........)
The boiler was installed 2 years ago, and a litre bottle of inhibitor was installed at that time. I'll install more just to to sure - its reasonably inexpensive.
wrote:

this
but
are
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You're supposed to collect it in a test tube over water, but that isn't practical. I've done this before by opening the vent very gently and applying a flame. Make sure there is nothing flammable immediately adjacent and have a wet cloth ready.

It depends on which product it was. Fernox MB1 is generally 5 litres in a container. IIRC, Sentinel is in smaller containers more concentrated.

.andy
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wrote:

Something that I've often wondered is what stops the flame going all the way back inside the radiator? I'm sure there's a pretty simple explanation about it (like lack of oxygen in the radiator stopping combustion within it) - but I've often wondered what stops it from doing so. Similarly with gas appliances - what stops it going right back up the gas main? ;)
D
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Lack of oxygen certainly does. There are also other issues which keep flames where you want them such as the speed the combustion front travels at any given gas/air mix.
--
Andrew Gabriel

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On Wed, 17 Dec 2003 16:02:26 -0000, "David Hearn"

Same answer in both cases. No oxygen.
Actually in the case of a radiator, there may be oxygen from dissolved air, but not a lot .andy
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David Hearn wrote:

The gas comes out faster than the oxygen can sneak back in.

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