Dave Baker wrote:

With all due respect, you're daft.

I'm actually a rather competent engineer who was hoping for reasoned opinion
on the merits of this vent.

Stick to racing engines. I'm an HVAC Engineer. I suggest you take it
off.

Take it off.

No thanks. As I say everything works very well as is.

So far.

Firstly, the water in the boiler system always has an open vent path via the
fill point at the bottom of the tank in the loft. If water can get down that
I see no reason why dissolved oxygen can't get back up it.

It's often on the return and it's commonly lower. The oxygen won't get
to it, it will corrode the radiators,


Secondly, The vast bulk of the water in the system is in the radiators and
that's where the vast bulk of any dissolved oxygen will end up. There is no
way for bottom fed radiators to have this oxygen removed than by bleeding
from the valves at the top. A bleed valve at the top of the boiler system
would surely do the same rather than having to have a permanently open vent.


In the event of a control failure, it is a safety device; it releases
steam, prevents the system becoming over-pressurized and bursting. In
your system, such a failure would probably now cause the contents of
the heating system to be discharged into the loft and the boiler would
dry-fire to destruction.

Nonsense. The system isn't pressurised other than by the head of water from
the loft tank. The contents of the system can't be discharged into the loft
other than by the same pipe from the bottom of the loft tank which is
continuously filling it up anyway.


It would be discharged into the F&E tank through the cold feed pipe.

It was pumping over probably because it was piped incorrectly.

Possibly but it was certainly ok for many years

You may think so. I do not. You didn't notice anything amiss, this
doesn't mean it was OK.

the system in 19 years was a new pump which was fitted by a Corgi plumber.

Ye're doomed, doomed I tell ye.


Now it's possible this was fitted to pump in the opposite direction from the
original pump but I can't instantly see how this would make a deal of
difference anyway. I'm open to suggestions as how it might. At present the
vent is on the return side of the pump so if anything I would think this
would give the least chance of pumping over.


I find your faith in a cheap safety valve to be touching.

They don't have to do anything in normal operation. If called upon to
operate in anger, a disturbing number fail to work. Many have been
dripping inconspicuously for years, the water evaporates from the hot
safety valve and the accumulation of limescale deposits concretes the
valve immovably shut. Have you tested the valve?


Kin 'ell! Is this a wind up? Leave it alone.

I have every intention of leaving it alone because it cause no problems as I
have made clear. Please try to confine yourself to the physics and
hydraulics of the issue rather than pontificating.

I have done. You're convinced you know everything worth knowing about
it and can't believe that someone else may know more.

Take it off.

Dave Baker
www.pumaracing.co.uk