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).
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?
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.
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
This gave approx 1/2 bar pressure drop, needing a small amount of topping
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
I'll check the valves carefully.
Could it be when the heating season starts, all the rads in the house are
If there is a dodgy valve, it might start leaking then??????
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.
To email, substitute .nospam with .gl
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
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
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? ;)
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